Would maxillary impaction of 3mm make a big difference in shortening the middle third of the face?
Now that's an interesting question.
What would be the threshold to not end up with the teeth burried under the upper lip if one with no gummy smile has maxillary impaction ?
I'd guess 5 millimeters of impaction would make a noticable difference if the length of the midface but such a big amount of impaction should never be attemped on a non-gummy smile.