Unfortunately I have no answers for you.

I do have a comment though----I have never owned, flown or seen a decent flying aerobatic (scalish) model in that size.
Going a bit further, I have drawn a 'personal line' of 650sq.in.. That is THE smallest I will even build.

The difference made by that last 100 sq.in. is hard to believe. But trust me it is there!

I do wish you luck however-----'cause short of a minor miracle that is what it will take.