Forgive me but if you simply shake the fuselage (forget the balancer) can you feel anything move or hear any noise? Another point is if you think the CG is changing Then how much does it change?
I enjoyed my Sig STA for many years but do remember balancing inverted was a bit tricky simply because the landing wires and the fuselage jury struts were always right where ya always wanted the balance pins and that combined with the curvature of the airfoil right there made subtle shifting of the points always a pain for accuracy. In the end It was easy to resort to good old fingertips.
John