I have not only tried boxing bugs, but I have played it many times. I love vector games.
I am not at home right now, so I can't tell you what my settings are.
However, the standard answer is that spinner settings are fairly unique to every MAME setup.
It depends on the hardware (Optipac, Mouse hack, etc) used, the mouse settings in windows, and finally the settings in MAME.
I'll look at my settings tonight and see if I see anything in particular.