There is no relation between the (size of the) bounding box and clipping, the usual bounding box (that you can set via the min/max vectors) is only used for collision detection. AFAIK you don't have access to the "visual bounding box" that determines clipping, but you can use the entity variable clipfactor to change the clipping behaviour of a single entity.
Btw. your code does not make much sense as CLIPPED is no "flag", but an "eflag", thus the is/set/toggle macros won't help here. Use the following code instead:
if(my.eflags&CLIPPED)