I'm gonna say it:

BALLAST!!!

Possibly the only benefit of a heavier airplane. Maybe there are better methods, but this is the most basic law of physics: F=ma

I am sure there will be answers about wing incidence, dihedral and anhedral, etc. But my personal experience is flying my airplane with 5000mah packs and 4000mah packs. It feels much lighter and more graceful on the smaller packs, but gets banged around a bunch in the wind. If I use the 5000mah packs I hardly notice it.