Ai works on a simplified flight model, mostly. One could look up up in the java classes how consumption differs from any player's behavior but that's way too complicated for this issue. I think, AI always has some sort of "optimum" engine management, can be assumed.
Having built the above mentioned mission, soon saw this was going to be a 3hr (? iirc) round trip, about at the edge of what a player in game can squeeze out of a Zero, with short time over target. Actually, that challenge is what this mission is about, as it recreated the actual thing, having to watch your fuel over vast areas of ocean, trying not to miss your (guessed) bingo point or you will not make it back.
And then there was AI.
And here I say: To get this done is a mission builder's task.
The fighters, when "set" to be attached to bombers on cover, will go into wild high speed turns and patterns, in total disregard that they will run out of fuel soon.
What I had to do was to build the fighter waypoints on their own, not connected. Manage their climb and speed and time it so that the'y still be resembling a force in proximity to the target. It took several loops of watching the AI fly and how the flight to target developed in terms of placement to the bombers, but you can get that done.
I did a similar thing in another mission elsewhere when I had P-51 accompany B-29 on a long raid. The problem there was the really high speeds necessary but it can be done with some invest into the mission.