As I recall the zamak R41 head is relatively forgiving of shave angles, until it isn't-- I had a lot of issues with it tugging, skipping, or biting right at the edge of my goatee on the corner of my chin, on a few of the toughest whiskers. I can see how the upper lip would be equally challenging. The steel version seems to clamp a little better, enough that I haven't had that problem with it.