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Another thing that might help: Try cleaning out any stringing within the ocarina's chamber. I read a note about that Nochii's message where he cleaned out the holes to improve it, and after testing it on one of mine that printed with the high note being a bit airier than the rest, it now sounds crisper.
I don't know if it'll be enough to bring the high note back, but it might make your notes just below the high one a bit sturdier.

I'll be printing another test version (v15) in the morning to see if the high note is stronger on that one :)