All things being equal, you would expect a heavier bullet to drop quicker, that's just basic physics.
Since we're talking 100 yards and bullets going 2700-2900, bullet drop isn't the main factor here. It's just variances between two different loads.
It's all about the barrel harmonics of the different load. The 180 grain certainly doesn't experience 5" more drop at 100 yards than the 150 grain.