Bounding boxes for entities other than players are hard-coded into the game dll and set upon it's creation, but you may still be able to change that with EV_VEC_mins and EV_VEC_maxs.
Bounding boxes for players seem to be constantly updated based on whether they are standing or ducking and not overridable by changing EV_VEC_mins and EV_VEC_maxs.
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No longer around. Thanks your support, everyone! As always: