If you're getting good arrow flight and are grouping well at 30 yards, I doubt your problem is with your arrows. I suspect it has more to do with anchor point/peep location.

As distances increase - especially out at 40, 50 60, etc. your anchor point is going to change slightly since your peep sight is raising slightly with the increase in elevation of your bow. Granted, we're talking very, very small changes, but those small changes are magnified as distance increases.

A slight cant of the bow, which may only be reflected as a right/left shift in point-of-impact at 20 yards of 1/2" could result in a change of 3" or more at 60 yards. A small change of anchor point at 60 yards, will result in the same type of inconsistency.

Field archers, who regularly shoot at 70, 80, and 90 yards, are constantly battling these types of problems