Balance will also have an influence on trim quantities. Start at 6-1/2 " aft of the top wing point and move bach to 6-3/4" aft and see how that works for you. If the wing incidences are close, and the c/g falls within that range you may want to experiment with up and down thrust a little. I wouldn't go more than two degrees either direction in the attempt to find what you seek.

Bear in mind that the 24" prop you are running due to a larger engine is having an impact of it's own that you will have to factor into the trim equation.