I don't see what was so hard to understand about that. When the wad hits the base of the shot column in firing the shot in front which has to me moved is held back by inertia. When you put the same weight of shot in a 20 ga as is in a 12 ga the column is 40% longer, put it in a 28ga & it is 75% longer. That means the shot down next to the wad have a lot more weight ahead of them to move. Trying to fire an ounce of shot from a 28ga would mean that hard premium shot, & pobably buffering as well was of far greater importance than firing an ounce from a 12ga.
No this has nothing at all to do with choke.

Miller/TN
I Didn't Say Everything I Said, Yogi Berra