Here's what happens with the OEM setup.

When you move the TX stick, both the aileron servos in the lower wings move the aileron they're rigged to whatever your TX stick movement tells them to. Lets say the TX movement says 20degrees. Both those ailerons on the lower wing move 20degrees. One moves 20 up and the other moves 20 down.

When the aileron on the downgoing side moves 20 degrees the OEM rigging pulls the upper aileron it's connected to 26 degrees.
When the aileron on the upgoing side moves 20 degrees the OEM rigging pushes the upper aileron it is connected to 23 degrees.
The OEM rigged Skybolt sees 3 different aileron movements from your one TX stick command. And that is caused by the way the pushrod is connected, mostly from the way it's connected to the upper ailerons. The lower aileron hardward actually is pretty close to giving the prescribed 90degree setup.