Re: NPOA and drift
Identifying it is half the battle, if you have an answer and you know what is going on, the correction is easy. Just takes practices.
No real rule of thumbs to work with, just some average behaviors we see, if you are slightly different then that is the answer... you shift right, push the shot right, hence you have to work on it.
I generally advocate your LOP being 1/2" shorter than the measured distance from the crook of your arm to the trigger. That should be with the stock in the crook of your arm with your grip and finger in place. Don't just extend it there and hold the finger straight and measure that is too long.
But it seems you are diagnosing your own issues which is good.