Just for your own sanity, next time you are at Lowes grab a roll of brown "builders paper". The stuff is cheap.....i think under $10 and it really is useful stuff. I never leave home without it when I take my smoothbores out.
It is very possible you are shooting under with no rear sight.....the tendency with just a front is to really bear a straight line down the rear barrel flat to the sight and if you think about it, no rear sight would ever be that low. Lowering a rear sight brings your shots down so if you are down that hard on it it's definitely possible.
You may need to "raise your rear sight" by changing the plane of your sight picture.......close your eyes mount the gun comfortably without an effort to squish down flat and then open your eyes. I would bet a dollar that you are seeing much more of the barrel than when you are shooting those turkey patterns.
It might be as simple as learning to see more barrel flat essentially raising your rear sight.
30yd patterns......just an average one. Ive been as high as 150 hits but very consistent.
20yds is nasty......and this is #5.5s......6's would add even more holes.