Mmm, no true, wrt the frontal arc not being restricted by rail gauge. But there are always trade-offs for uparmouring in this way. You have the extra weight, the balance of the vehicle, the cost - in materials, time to design and fit - and so on. I guess the question is: is it effective _enough_ to justify the trade-off costs involved? Off-hand I can't think of many examples of spaced armour in the frontal arc. The MkIV H, is kind of my poster boy for spaced armour - particularly in the turret and hull flanks - but it doesn't have that much in the frontal arc, does it? A plate bolted on the mantlet - but not really 'spaced armour' as such. I seem to recall they have a Swedish S-tank in the sheds at Shrivenham with frontal arc bar armour. But on that unusual vehicle it isn't going to interfere with your turret traverse and elevation/depression. It is the iron laws of physics again - if you are having to putz about with a vehicle to that extent (a bit like trying to keep an old banger on the road) then you might well have to ask yourself whether you have the right vehicle for the game you're in. And if your frontal arc is _that_ vulnerable you are thinking about applique armour, chances are you need to take a good long hard look at your fleet. Kind of the story for British tank production through the war really...