I duel a couple of my good friends regularly who are very average pilots at best. I tell them to hold on HOing on the first merge but any other chance they get to put guns on me, go for it. This gives me the opportunity to craft my merges away from the instinctual flying style of just pointing your nose at the red dot any chance you get which has given me a very strong MA style of flying.
There are 3 situations however I have come across where a HO is hardest to avoid. (Feel free to give me some advice or tips on these scenarios if you have any)
1) Deck merge (especially when slow). You can try your best to avoid the HO but if they really want to shoot you, they usually can no matter how much avoidance you attempt. (Are there any juke moves that will ensure a miss here?)
2) In a turn fight enemy out E's you and is above you and coming down at you. You have enough E to point your nose up at him which might work in a duel, but in the MA it seems this is futile.
3) Reversing a sharp turner. Early in a fight you reverse, say a spit9 or a n1k2, and come around and are 'waiting' for him to come into your front view and instead of him coming in, he finishes off his turn sharper than you anticipated and comes right up at you and shoots you.
Most other situations I feel like can be easily avoided without giving the enemy any tactical advantage.
If you are constantly finding yourself in head on situations, your tactics may be off. I'd go see a trainer and ask him to teach you how to avoid HOs and gain advantage in doing so.
Here's a very short film on how to avoid a HO and gain an advantage on the deck when a plane is trailing you.
http://www.speedyshare.com/810218191.html