Note the phrase "without expending enough energy that you give him a large advantage." If the other guy is a very good shooter, then you will be hit no matter how fast you are going and what direction. Theoretically, you can be hit while going five hundred miles per hour perpendicular to you opponent, if he's good enough. Obviously gunners this good are very rare, but the better the gunner is the greater the angle you ship must be from his in order to not get hit. This gives him a great angles advantage. Moreover, often you must pull hard at the last second to jink; this bleeds off a lot of energy and gives him an energy advantage.
The point is, if the other guy is a good shot and determined to head-on, you have two choices; you return fire, forcing the fight into a contest of gunnery rather than flying skill, or you can dodge his shot by sacrificing a great deal of energy and angle. Again, the better the enemy gunner is, the greater this sacrifice need be, and theoretically if he's good enough it will be impossible to dodge no matter what.
I have a challenge for you; come into my head-to-head server and we'll do a few fights. I'll make a head-on pass, but instead of returning fire you try to avoid it. I believe you will find that I'll either nail you on the head-on or else you will have expended enough energy (or given me so great an angle) that you will lose the subsequent dogfight.
