Face shots were eliminated (or had reduced lethality) in AW for one reason. AW did not have collisions. So without collisions planes could, and did, fly straight at and through each other. Squeezing the triggure at the last moment was just a matter of will. It was felt with face shots enabled the dogfighting would become a joke. So nearly every encounter started with two players flying directly at each other... "the merge". What a joke. That habit alone is probably responsible for most of the face shots in AH.
A head on (HO) is when two planes fly directly at each other. It's like a game of chicken which ends in a collision if one or the other does not avoid it at the last second. The face shot is simply an option during a HO. Although head on collisions do happen by accident, in AH they are mostly done by the free will of *both* players involved. If one chooses the HO and trusts the other to not shoot, it is a stupid mistake on his part.
Now I'm not a good player, as my score shows. But I have been at this stuff long enough to know what should be done (doing it takes skill, for that go see Levithan, aka: Dead Man Flying... a fine killer indeed). I can tell you aspiring air warriors (hey, I earned the right to condecend) without a doubt, and no accomplished player will disagree, that you must start applying the principles of air combat maneuvering *before* the merge. This is precisely at the time you would otherwise be engaged in the face shot.
So there you have it, good ACM and face shooting are mutually exclusive. I think, in a nutshell, it should be your last option. But it's your choice, don't blame others.
Now, one more thing. Those who tell you that you can avoid getting face shot *all the time* are full of beans. It will happen. There are those times you are suddenly face to face with a foe and do not have time to avoid... you better shoot. There are times like when I was semi-asleep at the switch and did not react in time... I bet I'm not the only one who snoozes and loses. Sometimes a plane I'm chasing reverses and I don't notice it until too late (I'm old yanno). AH doesn't faithfully show exactly what a plane is doing or even the direction it's pointing all the time. You will get face shot plenty of times... tough, deal with it.
We need a good training program. ACM means a lot more than HO, rope and Duke Cunningham's hitting the brakes so they fly by. (Yes, it really happened, and he's the one who did it... but he was out of options and a bullet away from death at the time.) So many six calls I've given when the person didn't do anything to avoid it. They likely didn't know what to do. Such a pitty.