I know CM LOS mechanics is suspect...but this?

[womble]

You fail to understand why I said outnumbered 5:1. There are five PzIV tanks that have potential LOS to the Sherman which itself has LOS to each one of the five PzIVs. If the Sherman has LOS to them, then all five PzIVs can also have potential LOS back to the Sherman, if they are able to spot the exposed part of the Sherman from amongst the trees at a range of about 175m, which realistically almost point blank.

4 of those IVs are within 5 or 6 degrees of each other. While the Sherman certainly isn't considered as a "point" for targeting, neither are the points (AIUI) sufficiently numerous to make all of the drawn volume a target. it's possible that all the points that do represent it are hidden behind cover from that angle. It's also possible (and you could check with your opponent if you wanted) that there's enough concealment that the IVs haven't spotted you properly, just stopped Hunting because they got a "tentative" contact. The fifth Panzer which broke to your right may well not have spotted you at all.

If the game however only considers the "centre of mass" of the tank as the ONLY targetable spot on a tank, then unrealistically the PzIVs will probably not have LOF on the Sherman because the centre of mass is probably out of LOS behind a tree truck.

It doesn't. I've had tanks fire at targets where the CoM was certainly out of sight.

[A Canadian Cat]

True re the hulldown case though I am not 100% on how CMx2 handles hulldown. Does the game apply a discrete "hulldown" status to a target

So, there was recently a very long and illuminating thread about hull down and an unexpected spotting out come - not at all related to your situation. From that, a couple of corner case defects were actually found in the game - again not relevant to your shooting situation but possibly to the spotting although I certainly cannot be sure but I suspect it would actually effect your Sherman's ability to spot the PzIVs but that is pure speculation on my part.

Getting back to what is relevant for the purposes of spotting - as in how hard it is to see a hull down tank there is a discrete hull down state for the purpose of a hull down tank becoming spotted. That effects spotting only. There are some efficiencies built into the spotting part of the engine so our computers can actually spend time drawing stuff and making troops and vehicles move around . There is no such thing once the bullets start flying. Once the shooting starts it all comes down to what the gunner(s) can see an how well they aim and once they pull the trigger the round is tracked using physics.

(eg. is target "hulldown", if yes apply -X% to hit)

I know many of us come from a die roll, look up results background but that stuff does not apply here. Just toss that out of your head. I am not saying there is no randomness in the game but it is just in a different place. There are no results tables. Repeat after me "there are no results tables" . It is difficult to change ones mental model of what is going on and since we spent years rolling die and looking up tables for results we naturally try to apply that to this game. I have learned over the last few years that just does not work here.

There is randomness in the Tac AI - between deciding which course of action to take. There is randomness in the spotting routines - the time it takes a unit to spot something will not always be the same. There is randomness in the choices the gunner makes when they are aiming. All this randomness will be effected by the pixel troops training, their leaders rating, their morale, their current threat state and on and on. So even here in the process of the Tac AI there are no lookup tables and results tables like we are used to.

Once all that has happened and the gunner has made "his" best effort at aiming at what he sees and he pulls the trigger the round is tracked using physics and it hits what it hits at the angle it hits and does what it does. No results table, no look up, no modifier - chuck that mental model

or does the game just consider whatever portion of the target is visible and smoothly scale things accordingly that way, with "hulldown" just being a general term we use to describe cases were a vehicle typically just has it's turret exposed to the enemy.

No, the game figures out who sees what and gunners aim at what they see. This is why, for a tank, you can get situations where the Tank commander can see an enemy but the gunner cannot. Heck sometimes the main gunner cannot see something but the hull MG gunner can and you will get MG rounds on target but not the main gun.

Each person in the tank can see what they see and if they have a trigger to pull they can aim at a target and let rounds fly down range.

What is more curious to consider are cases similar to the one I have illustrated. Can an in game object that blocks LOS, like a tree trunk, be positioned so that the object only blocks LOS to the middle of the target/vehicle, but leaves the the rest of the vehicle, on either side (left and right) of the blocking object, exposed?

Yep.

In this case to an observer spotting the vehicle, you could say that they could potentially aim at either the left or right portion of the target that is visible.

Yep.

Can this happen in CMx2? Could it be happening in the Sherman vs five PzIV example?

Sure. Probably. As has been noted there is probably very little of the Sherman exposed and given that the Sherman is not moving or firing there is a very high likely hood that the PzIVs have not spotted your Sherman yet.

[Vanir Ausf B]

True re the hulldown case though I am not 100% on how CMx2 handles hulldown. Does the game apply a discrete "hulldown" status to a target (eg. is target "hulldown", if yes apply -X% to hit) or does the game just consider whatever portion of the target is visible and smoothly scale things accordingly that way, with "hulldown" just being a general term we use to describe cases were a vehicle typically just has it's turret exposed to the enemy.

Ian touched on this already, but basically the game treats hull down status differently for cover and concealment. There is a concealment bonus applied to the hull down unit (or penalty for enemy spotting units, however you want to look at it). This probably is a flat modifier, and it is binary. You must be completely hull down to get it. Partial hull down does nothing for concealment. Cover bonuses are granular. They give a reduction to enemy hit % roughly proportional to the amount of tank visible. Partial hull down is good, full hull down is better.

As mentioned previously, there is presently a bug or two affecting how well fully hull down tanks spot but as far as I know the cover aspect of hull down is working properly.

[akd]

Cover bonuses are granular. They give a reduction to enemy hit % roughly proportional to the amount of tank visible. Partial hull down is good, full hull down is better.

I don't think there are any % bonuses involved. Shorter objects are simply harder to hit. If dispersion or range error puts your shot 1m low from aimpoint on a hull-up tank, you still get a hit. If the same happens with a hull down tank, the shot impacts the ground instead.

[Vanir Ausf B]

That is probably correct, although the end result is the same.

[Lt Bull]

Well my opponent has just submitted the next turn to me. As expected, the PzIV that was veering off to the right moved in to the LOS of the Sherman and got nailed, no surprise there.

What was surprising was what happened next:

CMBN_LOS3.mp4

1) None of the remaining four PzIVs, (the front three of which were unhatched with their commander spotting from about 150m-170m away) were still APPARENTLY able to spot the Sherman which had just fired two rounds from it's main gun and bursts from it's hull MG.

I say apparently because I can not be sure if, from my opponents perspective, whether any of those PzIVs have indeed spotted/have established LOS to the Sherman. I am guessing they don't otherwise I would have expected them to fire at the Sherman (but only if the game does indeed allow tanks to target partially visible portions of tanks in situations unlike the "classic" "only turret showing" hulldown situations).

2) After nailing the PzIV that veered right, the Sherman's radio operator then was then able to aim the hull MG at both commanders of the front three PzIVs, killing the front two.

Here is a movie from the perspective of the Sherman radio operator/hull MGer. (I disabled the translucent tree mod and toggled show tree trunks only).

CMBN_LOS4.mp4

Looking at the movie, if the tree trunks you see in the game actually do block LOS and LOF, then there is no way that hull MGer could get LOS/LOF with the hull MG to the first and third PzIV it fired at.

Here is a movie from the perspective of the second PzIV which seems to have the best possibility of spotting the Sherman. I toggle the trees (alt+t) so you can see the difference.

CMBN_LOS5.mp4

With just the tree trunks showing, you can see that visually in game, the hull MG of the Sherman is exposed to the PzIV and not blocked by a tree trunk. It is understandable then that the game (in theory) allows it to fire the hull MG at the TC. However a substantial portion of the Sherman is exposed either side of the tree trunks.

However with the foliage showing, you can see the foliage does cover the upper part of the tank including the radio operator/hull MG position. You could argue either way that no LOS from the Sherman should be allowed or that LOS from the radio operator position could still exist between the abstract spacing between the foliage that is represented as a solid. Still, the lower part of the hull seems unobstructed. If anything, this is what the PzIVs should spot and at least fire at, regardless of whether the Sherman has LOS to the PzIV.

Here is a movie from the perspective of the first PzIV that has it's TC killed by the hull MG. You can see that the LOF from the hull MG pass through the tree trunk represented in the game.

CMBN_LOS6.mp4

So this seems to be the inverse of a hull down position, whereby the turret and upper hull is obscured and the lower hull exposed. Is the game engine handling things realistically?

No, the game figures out who sees what and gunners aim at what they see. This is why, for a tank, you can get situations where the Tank commander can see an enemy but the gunner cannot. Heck sometimes the main gunner cannot see something but the hull MG gunner can and you will get MG rounds on target but not the main gun.

Each person in the tank can see what they see and if they have a trigger to pull they can aim at a target and let rounds fly down range.

Maybe it does but what is visually represented in the game does not seem to be what determines this ie. there is some abstractness going on with the graphics.

[A Canadian Cat]

So this seems to be the inverse of a hull down position, whereby the turret and upper hull is obscured and the lower hull exposed. Is the game engine handling things realistically?

Looks like it to me.

Maybe it does but what is visually represented in the game does not seem to be what determines this ie. there is some abstractness going on with the graphics.

There is a bit - mostly it is what you see is what you get but sometimes a shot gets made though tress that looks like it should not. In fact the light and heavy wood ground are probably the most abstracted. Some times I look at how they look in game and I think "how could any of those low scrubby things stop any bullets or block my LOS at all". If anything the additional abstracting is in favour of your tank staying hidden. Your example in one case seems like the hull mg is firing through the tree trunk so clearly things do not match up 100% with WISIG. But really though, if you play the game like it is totally WISIG and don't get distracted the odd time it is not you will be happy

Nice animated GIF showing your hidden tank BTW