ta0, i made the same test with my top and, with a little surprise i discovered that the center of mass is very similar to the throwback, between 60-65% of the total height of the top.
poptop, your work is very interesting for me, I'm not a good player (for now i hope) but i like a lot to make yoyo, tops, modding ecc so any help is welcome for me :-)
Maurizio