A lot of Head-On complaints are dependent on the point-of-view of the user's front end.  I think it frequently happens that from the shooter's point-of-view, it's a front quarter shot, while from the victim's front end it's much closer to nose-to-nose.
It also happens that the shooter will say it's not a Head-On because the intended victim tried to avoid the Head-On.  I had a fight with Joey's P-51D (of tonyjoey) in a 38L the other day, and he tried for the Head-On shot in the initial merge.  I tried to avoid the Head-On, took a ping, and went on to shoot him down.  Then I asked "why did you HO on the initial merge?"  He answered "I didn't HO, that was a front quarter shot."  Yeah, only because I didn't try to HO too. 
 