It isn't your stones. The 650 may be a few, 2-3, thousandths of an inch thicker than your 1100, which will help. A .01" difference in stone thickness will be fine, .02" will be noticed if everything else is perfectly repeatable. The bigger your bevel the more stone thickness matters. I would guess your angle is changing because the knife apex is moving. Work on keeping the knife in the same spot while you sharpen and flip, consistency is what you are working towards.