OK, I have been watching these "differential" threads for a while now, and I have to chime in. Vertical up lines is not the place to set your diff. The reason is simple. The wing is at 0 degrees aoa and is producing 0 lift. (symmetrical airfoil) Any drag (induced or parasitic) created by the ailerons will be equal if the throw is equal. If your plane is wobbling on up line rolls, then the aileron geometry (or rudder trim) is not right to begin with. The place to set diff is straight and level and cruise speed. The draw back to this....that is the ONLY attitude and speed that the diff will be right. Speeding up, or decreasing the aoa will require less diff. Slowing down or increasing the aoa will require more diff. It is a compromise to get the plane as close as it can.

Aileron diff does not reverse when you are inverted. To keep the nose pointing straight, in a full scale Pitts and Decathalon, when rolling from inverted requires the same rudder input as it does from upright. Up right...right aileron, right rudder. Inverted...right aileron, still right rudder. (pilots perspective)

Hope this helps,

Bryan