I have exactly the same problem.
With non-retracted foreskin I only get skin stretch (useless?)
With retracted foreskin, the grip HURTS too much to get a good stretch.
Hence, I do never get a good lig stretch.
I will therefore skip stretching from my program and basically only do jelqing until I figure this out. Either I conclude that the skin stretching is of any good, or I learn how to grip with foreskin retracted.