Why can ground units only be attacked by a single air unit each turn, when ground targets can be attacked by multiple enemy ground units each turn, and air units can also be attacked by multiple enemy units each turn? Not only is the idea of one ground unit, one air attack each turn unrealistic, but it also leads to gameplay tricks like sitting an air unit over a ground unit you don’t want enemy aircraft to attack, in which case your ground unit is only open to air attack when the aircraft sitting on top of it has been shot down. An easy way round this would be to have air units attack ground units on adjacent hexes as they do when attacking other air units or as ground units do with each other. That way a fighter aircraft sitting on top of a friendly ground unit would still defend it (as anti-aircraft guns do) but would not completely close down the possibility of any enemy air attack getting through.