The reason for avoiding the HO came about originally in sims in pure 1v1 duels on the INITIAL pass, where a lucky single round would stop the fight before it even started. Usually "cold guns" (or "cold pass") was called to allow both pilots to set up their merge to their preference and allow for a truly equal-ground starting point. Once the merge occurred, anything was (and should be) fair game. And why shouldn't it be? If the opponent can gets their guns on you after the merge, that's YOUR fault. Head-on passes are actually a valid tactic and they were used in WWII, especially by aircraft that grossly out-armed their opponent (namely the Germans in their Wurgers).
This rule has been true in every single flight sim I've flown (including Fighter Ace, CFS1+2, WWII Online, etc.)... yet for some reason this community has a homophobic aversion to EVERY type of head-on pass for no logical reason, as if it's somehow dishonorable.
Never mind the fact that it quite literally takes two complacent pilots to perform a head-on pass, this is a air combat simulator. Projecting moral superiority and crying about a head-on pass while attempting to kill your opponent by shooting him in the back is most hypocritical stance I've seen yet in a flight sim.