Open up the chokes and be happy. I have a Ithaca 20 that I had opened up to .010 and .020. Shoots well, too well. Partners now claim that my misses are my fault and not the guns. So be careful.
I also find that the quality of shell and shot in particular make a much greater difference in the 20 than the 12. Have you confirmed tight patterns with a few trips to the pattern plate? If you see real tight patterns there then you know that opening up is the way to go. This would also confirm that point of impact is not way off from your expected point of impact. If your gun is shooting 6-12" higher than you expect then you are only using the top or bottom third of your pattern for most shots. Pays to know where it is shooting.
