I've heard arguments from both sides for ever. I think the CG doesn't change, but balancing a low wing inverted is easier that rightside up. Because of more instability right side up, you're CG has to be right on. Within a mm tolerance or it will spill out of balance. That just my take. But here is my dilema. I have a 1/3 scale SIG Spacewalker. It is technically a low-wing, but it has such a deep dihedral that balancing inverted is actually less stable. I haven't measured the dihedral but if you were to draw a line from wingtip to wingtip, it would pass through the pilots head!! So, how would you balance it?