I do that on RC bipes as well - slight negative incidence in the top wing.
I think it's similar to toe-in on the main landing gear on your tail-dragger. If the plane yaws left (on the ground), the right wheel sees more drag/friction on the ground (than the left wheel) and tends to correct, pulling the nose back to the right.
In flight, I suppose, if the plane pitches up, the lower wing sees more induced drag than the upper, and tends to counter the pitch.