Garry , there is proof for patterning at 25 yards but none that I know for 30.
As to the second part of your question , consider this. I do not know the answer directly , but I can provide reasoning to an educated guess. The tightest choke 20 ga that I know of is in a C that I own, .028 “ , certainly a tight choke when a usual 20 ga full choke is about .020. The .028 in a 20 is a 4.55 percent choke.
Your 28 ga at .022 “ constriction is a 4.0 percent constriction. If it were constricted to 4.55 it would be a .024 “ constriction. We know that as gauge reduces, it requires less constriction of the barrel inside diameter to achieve the same or similar percent of pellets on target , that is why full choke on a 12 is .030 or less and full choke on a 20 is .020.
So , your 28 at .022 is certainly full choked and may be at the effective limit of choke boring , any more and the jamming of shot at the constriction could result in more flyers and a broader pattern.
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