I only bopped my nose once with my thumb while shooting slugs prone. It was amazing how I learned not to do that again.My thought on the pistol grip was to reduce the chances of bruised/bloody noses from the thumb on the shooting hand.
An entire generation of GIs shooting short-stocked M1903 Springfield rifles learned how to fix that problem.
Just shift your shooting hand thumb over and rest it on the knuckle of your trigger finger... That'll do it.