I have never seen a heli that didn't have its tank mounted at least close to being centered, yet they usually have header tanks. Maybe a few scale heli's but I don'tthink I have seen a serious scale heli model for a very long time. Even so a header tank will not correct an off center tank, just as raising a fuel line well above or well below the engine will not affect the pressure. The header tank is there to keep a full tank so that very aggressive aerobatics will not cause the engine to pick up air and foamed fuel.