I REALLY like this, and I have some ideas!
Can you make it allow multiple attack modes? For instance:
UFO attacks, and you have standard and aggressive attack modes available. It defaults to standard, wherein it gives the UFO the weapons priority and automatically engages at the UFO's weapon range. If that's too far away for you, you can select aggressive and get in closer.
I have some other ideas:
* UFO escape timer begins when UFO enters X-Com weapons range. If it's faster than your ship you can't flee, but you might be able to scare it off.
* All UFOs (except any that have no weapon) can attack X-Com craft but will be slow to respond, mostly they attack patrolling ships and anything spending too much time near them.
* When you engage a UFO it begins its escape timer, but sometimes when the timer ends it opts to engage aggressively instead of escape. If it does this, it may run closer to your interceptor and put it in danger.
* You always have full control of the battle when your ship is faster. When yours and their ship are the same speed, neither party can flee unless the other is also trying to flee. If the UFO's run timer ends and it chooses to flee, it will silently remain in flee mode until combat ends or you opt to disengage. Once it begins trying to flee, you can no longer close to a shorter range with it than where you already are.
* Maybe this is getting too complicated but I think it would be fun to use yours and the opponent's speeds together to determine how fast the craft approach each other. When your craft and the UFO are in mutual agreement to close each other, you might find yourself getting up close very rapidly. On the other hand, if you engage a UFO going almost as fast as your interceptor and the UFO is in travel mode (not engaging or fleeing), then you'll close the gap very slowly, possibly buying more time for its timer to finish and give it control of the battle.
