About gun convergence

[notimejeff]

Just seen a Discovery documentary in which a WW2 Spit/Hurri pilot said that when the squadrons received their planes they would unilaterally alter the gun 'harmonization' from the standard 400 yds so that the inner guns converged at 200, the middle guns at 250 and the outer guns at 400, thus giving what he called a lethal cone.
Well this was news to me. If anyone has heard of this could you say where you heard it, as it would be good to verify this. Was this practice widespread or just confined to some squadrons? Thanks for any info. BTW it might make a good mod if when the more pressing issues are resolved.