Minimum convergence?

[robtek]

In a 109 the convergence is rather less important, even with the convergence set to infinity the trajectory would still be in a triangle roughly 50cmx50cmx50cm, plus of course the ballistic diversions.
For wing mounted guns i believe that the lowest distance setting of the gunsight (150yds) would also the reasonable shortest possibility for the guns.
For the german wing mounted guns the fixed distance of 100m would fit.
If you are closer you shoot with a slight offset, using effectively half of your guns and the other half by chance.