The hand is a sympathetic organism; what one finger does, the rest will do, which makes it difficult to isolate the trigger finger. The most common mistake shooters make is squeezing the whole hand instead of just the trigger finger, which is why competitors like short-trigger actions.
The “dipping” caused by whole hand convulsion, is often attributed to anticipating recoil or “pre-ignition push,” which I believe is true for new shooters. However, once it’s realized they can control the gun’s recoil, I believe experienced shooters shoot to 7 o’clock (right hand) or 5 o’clock (left hand) because they’re trying to fight how their hand wants to function, i.e. the whole hand squeezing as one unit.