I can across this problem in spades when I was building a night hunter mission - 6 defiants (height 950) attacking 9 He111 (height 1000).
I had them fly under the bombers;
With Defiant gunner skill = novice, average and veteran, very little damage to He111s, they all kept flying to their bombing point. kick up the gunner skill to Ace and bombers were falling out of sky like flys! To get a happy medium, i had the first 2 Deffy's gunner with Ace skill ,1 Vet, 1 novice and the rest average. kinda seemed realistic ??
A related problem seems to be the fact the AI gunner won't target the closest enemy aircraf!
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