I didn't notice which dualsky motor and prop you were running, but why not use the 12T- APC 20X15 combo that many of us are using on more "standard" pattern designs?
The next version may have just that setup on it. The setup I used initially was the same setup that Chuck Hochhalter used last year to take 3rd in intermediate. I based my design on that setup and went from there. IMO, what I was lacking was pitch speed. IE< I could not get a prop in the right dia range with the right pitch to get the speed in the correct range.
The next airplane will likely have the more common setup on it, especially with the improvements that are coming to the bigger motor.