Actually, it ocurred to me I could avoid the two collision checks thing entirely by not using ent_move to move the model. Instead, manipulate the models X,Y,Z coordinates directly.

Like I said though, not that important to me right now. I mostly wanted to know if a) I was mistaken about there being only two sizes of collision hull and b) that this issue is known and will be addressed in future versions of 3D Gamestudio.