Mr.Ed, did I hear you saying zero, what model, early or late?
Early models had low velocity cannons, which sure does suck

Like in early 109s, which had MG-FF, if I now spell it right...
If you compare Hispano (brits lil' 20mm toy) to 12.7mm Browning M2, I think you would see Hispano have better range and so on..
Hispano has very good punch in it, which will shoot those 20mm shells very far away, even longer distances than 12.7mm bullet, because it has more mass in it, with closely same velocity as 12.7mm.
20mm also has better effect than 12.7mm from long distances, when it has bigger mass and explosive.
What do you do with bullet that just stucks into the airframe, making little hole, if you can have a bullet which makes bigger explosion while in that little hole

About ranges and other blahblah.. you can have a look on tank guns.
Which makes up for more effect/range, 37mm or 50mm?
or 50mm vs. 75mm?
(why do we do bigger than .50 caliber ammunition then, if .50 caliber is more effective from range than 20mm?)