I know there's been plenty of discussion on the vulnerability of open-topped vehicles in this forum, but I'm not sure if anyone's raised this particular aspect...
Let's say you have a Nashorn in a good hull down position. The gun is depressed and the crew compartment is basically parallel to the reverse slope of the hill. This not only creates a situation where there's very little of the forward portion of the compartment exposed, but any penetration will punch through the facing armor and fly off into empty space over the crew compartment. Basically, unless a crew member's head happens to be in the way (or the weapon is damaged), a Nashorn, Marder or "Suka" could take hits like this all day (alright, the crew might panic a bit, but...)
What about a tank? Same situation with regard to the gun and crew compartment orientations...but a penetration of the gun mantlet has the shell ricocheting off the roof of the turret and tearing up the inside of the vehicle.
This said, are hull down O.T. vehicles too vulnerable (relative to tanks) in CMBB? Maybe we should see more hits resulting in "gun damaged" than K.O.s?