150 Meter convergence mens at 300 meters bullets are further apart than gun barrels are. My accuracy in S.E.5 jumped when I set it to 500m (just shoot straight). May just be me.
I remember some thread(s) from a few years ago regarding convergence settings, but unfortunately I don't remember the eventual conclusion. However, the gist of it was that, whereas we generally think of convergence in WWII terms as a horizontal concept as the distance in front of the plane at which the bullets from guns on one wing cross/meet with the bullets from the guns on the other wing, for WWI aircraft convergence is actually a vertical concept - i.e., the distance at which the bullets from the gun(s) drop back across the sight line (having been fired slightly upward initially).
I'm not sure what's right, but the latter (vertical) concept makes a lot more sense to me. The horizontal (WWII) concept never made sense to me when talking about 2 nose-mounted guns that are only about a foot apart, and it can't even possibly apply to those early planes that only have one gun. Given that in RoF you can set convergence on these early planes that only have 1 gun, it seems to me that the devs must be using this as a vertical concept, not a horizontal one. (Even though they use an icon/symbol for it in the hangar menu screen that depicts it horizontally, that's probably just so it would be understandable/recognizable by most people.)