If you don't balance it inverted, you have to figure out if you're high wing plane is level when supported at the balance point? In other words, it might be a little nose low or nose high, and that can make a big difference. A lot of guys don't know/haven't figured that out yet, and there could be quite a bit of variance regarding where the CG actually is from one extreme (nose down) to the other (nose up).

Upside down high wing plane, the balance point will be where it's supported - or the plane will fall one way or the other - no different than you would expect a low wing plane to do when balancing one of those right side up.