I would not go with any tighter of a choke, especially if you are using Hevi-shot or one of the other heavy weight shotshells. I have tried numerous chokes and shells over the years, use to think years ago the tighter the better, but that is not the case.
If I were you, and I did anything, I would probably start by trying different shells. But with what you have now at 30 yards, I agree, that is not bad.
Good luck with your chase for that great pattern, we have all been there and done that!!! I wish there was a magic answer to give you, but there is not, as I'm sure you know, what might work great in my 835, just might suck in yours.