Your explanation is correct. For most models it's an adjustment of having the aileron that travels upward have more travel then the aileron that travels down. This is because the downward aileron produced more drag then the aileron that moves up. The correct term is aileron differential. If your airplane has dual aileron servos you can mechanically offset your servo horns to do this mechanically or your transmitter most likely has an adjustment for aileron differential. If the airplane has a single aileron servo you must do it mechanically. Here is an example of mechanical differential, notice in the picture the ball links are positioned slightly aft from the servo arms center.