I think its like the ECP mod. You only see effects to a certain distance that you set like 300m. Except when your not inside that tank you see the exterior textures and if you are "in" the range which would mean being in the tank you see the interior.
Maybe I'm wrong though as I have no idea how BIS coded it.
But the interior textures are for the player only and so are the exterior ones. I bet the AI would be content to blow up any gray colored box that came its way from the .p3d workshop. ;D
But I like the idea of getting rid of lag even if its a small amount of it.