Pyro once said I vaguely remember something about collision sizes only being valid if they are powers of 2? Or maybe it was acceptable max collision size if you change the constant? There are some things just hardcoded into the game that look like they can be changed but just can't, perhaps the max collision size is one of them. Try setting the max and the collision size of your tanks to the next highest power of 2 past the default max. I could also be crazy and my brain is making this up, so if you find it doesn't change anything then I'm definitely just wrong.