Fist Rotation

Hey y’all I have a question. When I’m throwing my cross or jab my fist is usually making contact when my thumb is at about the 4-5 position (think of a clock). My coach is constantly telling me to rotate my punches more and it just doesn’t feel comfortable for me at all to go much past where pictured. I don’t want to doubt him but my question is wether there’s any real benefit to basically having your fist full vertical or is it just a preference thing. It just doesn’t feel right when I’m over rotating and I lose power.