On the Fw 190, the closest pair are in the wing roots, maybe 3 meters apart, while the outer pair are even much further. On the Bf 110, maybe 40-70cm between all of them. I set the convergence to maximum, 1000 meters. The inaccuracy in the shells themselves are bigger than the distance between the barrel, and having convergence makes them cross each other's path outwards, the same disadvantage that wing cannons get (but less extreme). I am sure that in reality they used no convergence at all, since it was so close, and it was about cannon shells anyway.
The longer the range, the more effective the larger caliber shells are. The problem is of course, hitting anything. The 108 shells have low initial muzzle velocity, but their massive weight makes them overtake the 151/20's (which slow down faster from air resistance) after a few hundred meters, albeit with more projectile drop.
I love the nose mounted weaponry, and I love even more not having a propeller to have to sync-shoot through!
Firing both 151 and 108's at the same time seems to give no problem with stability of the plane, and their different paths (elevation wise) and large ammo supply increases the chance of a (brutal) hit. The technique I am working on in general to hit a plane of imprecise range and speed, when in 6 o-clock true chase behind him (he running away) is to walk the fire upwards. A 20 or a 30 is bound to come down on his plane if he's flying straight. They certainly have the speed advantage in later war scenarios, but having this firepower makes it possible to have a big shell catch up with them real fast before they get out of range
Absolutely though, the 151's are potent weapons. But the 30's are even much more potent, and they get to the target as fast as the 151's if there's a few hundred meters involved. I'm going to try to learn how to shoot both of them at any ranges.