Allow flying monsters to become immune to melee attacks

Flying creatures should have the option to become immune to melee attacks. To do so, they activate their "fly mode" and hover above ground. I always found it puzzling that BG2 dragons that have wings cannot fly above ground or fly away when they get seriously injured.
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So to attack you, they have to come close to you, in the range of your melee attacks.
So... no. No immunity for flying creatures.