Sure.
entity.lua: (I also added drawing_box)
before:
collision_box = {{-2.5, -2}, {1, 2}},
selection_box = {{-2.7, -2.2},{1.2, 2.2}},
now:
collision_box = {{-1.5, -1.5}, {1.5, 1.5}},
selection_box = {{-1.7, -1.7}, {1.7, 1.7}},
drawing_box = {{-1.5, -1.5}, {1.5, 1.5}},
After some more work I also resized the graphic terran_bunker_sc2 to 160x160 to make it fit better, it is not perfect but works for me.
I hope this helps you.
Edit: Seems like I changed the values a little since I last tested it. It does work, but the collision/selection box and the graphics are totally out of line. I will try around a little and post the new values once I find some that fit better.