I'm not surprised at your results. My only suggestion would be to try a few less grains of powder if possible to give more room and possibly a tighter pattern. Low and slow usually beats high and fast. Shotguns do best with lighter loads, not max ones, and more than 1 0z. in a 20 in a general sense has never made sense to me. Too much recoil, and 3" mag 20ga. loads are expensive anyway, even if loaded correctly. In the proper gun however, I can see their value, i.e., late season phez, etc.

Imagination is everything. - Einstein