Groupings?

Hop-up set-up or settings? The adjusted the settings so it would fly straight for each weight. A different (or better) set up only serves to extend the range that the BB remains stable and straight. At the ranges the tested, I bet you would see a similar result regardless of the hop unit used.

After all, that's the point of an experiment using controls. It doesn't necessarily judge best performance with whatever parameters, but it does serve to illustrate the variations that are present in each weight of BB.