I assume the captain's button to take full control and disable the FO's side stick is almost never used so would not be instinctive like taking over with a yoke. If she was using left stick and he countered with right stick to prevent hitting the left wing but didn't press the disengage button how would you add his right input to her left? You said it is additive, not averaged up to full stick deflection. What you said seems to say he could not counter the left aileron without disengaging her side in the above example. Is that correct?