Something else to consider, if your guns are set to converge at 275.........
At 400 out, your shots have already converged and crossed each other, and you are trying to hit his left wingtips with your right cannons (and vise versa), but they have probably fallen off that far from convergence and are falling below him. By the same token, if he's at 200, your shots havent converged yet and your rounds could be passing right over his wings and to either side of his canopy without hitting. These arent MG bullets with nice flat trajectories. You need to be aiming AT the convergence point, firing when you reach it, and trying to stay right close to it. Leading a target with those 20mm they will drop hard. If your convergence is 275 you should probably be shooting at a distance of 175-225, depending on how many Gs you are pulling in the lead turn (which is why, unless I'm in a tyffie or tempest with 4xhispanos, or a spit, I prefer lag turns and wait for a level shot with cannon-armed planes).
Since target ranges between 400 and 200 dont show (and this is just my opinion), you are far better off setting your convergence at a point you can be fairly sure of (either 400 or 200) and know from your rate of closure how close you are, firing just before and after your range counter clicks down to convergence range (in other words, if you set at 400, and you see the range go from 800 to 600, when you think its about to change to 400 squeeze the trigger so you are already firing when it rolls down to that 400 mark).
