#1.
what I mean by slipping hips is that when I get down, my hips turn or rotate, getting close to a supporting leg.
I think they should be kept neutral, no turning or rotating to either a straight, locked out leg or a supporting leg.
#2. Am I sitting deep enough, compared to mastery?
#3. Does pelvic tilt matters here? If it does, which is correct, PAT or PPT?