All the counter rotating propellers I have seen had more pitch on the down wind side, if you look at a Volvo counter rotating outdrive for boats, it is quite severe and more critical, water being 800 times more dense than air...
You are correct to assume the lower rotor needs more pitch, the upper rotor is shifting the apparent wind, or relative wind upward and therefore the need for more pitch. There was an Austrian company that use to make a contra rotating prop for ultralights, they said that the distance was critical to performance and had to be tuned to within less than a mm. They said it made a significant noise when even slightly out of spec...
In the RC coaxials I have seen, the separation between rotors is fairly large due to interaction. The full scale coaxial helis seem to have less, so maybe this distance recedes with higher Reynold's numbers and lower rpm?
I flew some coaxial RC autogyros and the rotors needed separation at least a quarter span of the rotor radius. I think this has more to due with having enough space for clean entry of airflow to the top rotor and can probably be less space on a driven system like yours.
How did you arrive at the spacing between rotors?
Also, have you thought about strapping some long spars in a cross formation under the skids to allow longer tethers?