Gun Convergance?

[SEE]

Looking for some advice about setting the gun convergence on the Spits. The default is 500m for both machine guns and cannons but should these be the same and set at a much lower distance? I read that the Mk1 Spits had their machine guns set at around 200 ft but not sure what the cannons convergance distance should be (when fitted). I am wasting far too much ammo trying to get the deflection angle spot on when aiming at a very small target in the gunsight but also find it damned hard to get a BF109 within 200ft.