Ines yep, when you sit your pelvic tilt lengthens the back line of your body (and consequently your chastity belt), so if it fits tightly when you're standing up it will put pressure on other areas when you are sitting. You can only bend and shape a chastity belt so much, at the end of the day it's a rigid structure and your pelvis is designed to move in three dimensions.
I've not had much success with rigid belts, we experimented with adapting a sliding front shield to a rigid bum strap but it ended up pinching in all the wrong places.
Maybe this is one for the "future of chastity belts" thread... Something that allows lengthening the back of the belt while still maintaining security at the front.
