I would just try different ways to stretch the skin very very skin and different ways to stroke the razor. Have you tried the scything motion? It's described in the WIKI and it's a great way to use the razor. I actually do scything motions through out my entire shave, it's just the way straight razors were intended to be used, I've seen barber's videos that mention this is the way the razors were meant to cut hair.

You pretty much slice sideways very very lightly while you stroke the razor either up or down (depending on the pass: WTG, XTG,etc).