I wouldn't worry about it...
The last couple of times I returned the stock i barely had KR and that was on tip in, not WOT, which is pretty typical .
IDK how big your tank is but the corn will definitely suppress knock.
Did you put the 1.2 gal of corn in by itself or did you top off with 93?
Look at the bright side, there a few guys on here that would love to have your problem.