Big? its not really that big, its roughly the same size of the default grenade but with a handle
I dont think i can make it smaller without making it look weird
I reduced the size of the top to 3x3, it just doesnt feel right for me:

This is the normal grenade version in-game (i painted mine black in the handle):

It looks decently sized for me...
Never had any trouble with it taking up more space than it should, and its also not too big to be considered an unfair advantage