Joe,
Even a "perfect" design may require some rudder - elevator mixes for knife-edge. This is because of the spiral slipstream from the prop. Each stab. half sees this and it makes it seem like they have different incidence settings when in fact they don't. If everything else is correct trim-wise you should end up with an equal amount of mix for both rudder directions. The plane will go to the gear in left rudder knife-edge and to the canopy in right rudder knife-edge so you will need to set up a small amount of left rudder -> up elevator and right rudder -> down elevator. You SHOULDN'T need throttle -> rudder mixes. Sometimes they're unavoidable but try to do everything possible (mechanically) to avoid using mixes.

John Pavlick
Team Black Magic, Tech-Aero Designs