I am still figuring out my H9 Sukhoi. There is much debate about where the CG should be on my plane, but I suspect mine is a bit tail heavy because my experience is similar to yours -- flies great in all modes, then a real handful to land.

The post that caught my attention in this thread was the one about elevator input needed for inverted flight. I too, need virtually no input to maintain inverted. If that fact equals tail heavy, then I may experiment with moving my batteries around to see if I get any improvement.