I was taught not to actually move my butt where it is on the bench, so I don't.
I've tried not shifting my weight on the bench at all, which I think causes more pain. I can shift all my weight to that end of the piano but I'm pretty sure I've read you are not supposed to do it that way either. I've read that you need to "lead with your head" and "bend from your hip joint" not waist.I don't quite understand what that means. I've tried to do something like that to no avail.