How can I make my girl's booty clap louder?

Is it just based off of butt size or is it more of a positioning thing? My girlfriend and I usually do doggystyle since I'm a big fan of her butt. She has wide hips and a pretty huge ass in general, but she lost 35 pounds since we've been together. It used to clap louder sometimes, it seemed like when she was standing and bent over a chair it was louder, and it made her boobs clap together too. That was on vacation. Now it's not usually loud at all even though her butt is jiggling all over the place still. Usually now we do it where she has one knee up on the bed or both knees.