I don't know much about percentages and such or 20 inch patterns or whatever, but my 28 gauge has improved/modified chokes and it seems I must be no more than roughly 20 yards for standard loads of #6 shot to be effective.
In contrast, my full choked .410 is ridicously effective on pheasants and mountain grouse out to 40+ yards even with 2.5 inch shells. I ain't no expert, and this is a small sample but I think choke makes a big difference in effectivness.
