When you dial up the A2 sight a bit - do you have much side-to-side movement of the drum? I can move the drum 1/8" side to side. It's like the threads on the drum ring don't work properly with the threads on the sight post.
From my experience with a surplus milspec A2 rear sight kit and a newly manufactured Luth-AR A2 kit, they both have some side-to-side play in the elevation wheel. I assume it’s normal.
White Oak Armament can install pins that eliminate the cant. Accuracy Speaks welds up a bump on the rear sight housing, then files it down to get alignment.