The attack bonus from Napoleon uses the activateUnit trigger to make changes. This can't work defensively. However, the bonus I used is in the resolve combat trigger, so I can check if the square is shared at the time of combat. However, once combat has started, you can't change the attack and defence of the units in question (I think I tested that at some point), so I damage the units directly instead. We could change attack and defence values during combat if we calculated the combat with lua, and simply set the winner's health to what it 'should' be, and the loser's health to 0. I don't think it would be too hard, but I didn't want to do it.