[Juha]

IIRC Finns tried first to eliminate the gunner and then
a) high side attack aiming where wing merged to fuselage because 20/MG151 ammo was capable to penetrate the side armour of Il-2 and one was able to punctuate the fuel cells and ignite the fuel or
b) shoot the plywood tail/rear fuselage to pieces.

Now Il-2 was a hard nut and not easy plane to shoot down and could absorb great amount of hits and survive but it wasn’t impossible target and sometimes it was possible to get multiple kills on one sortie.

To give some info of penetrative power of 20mm AAA
20mm AP round of Flak 30 and 38, the main light Flak guns used by Germans, was able to penetrate 20mm of homogenous armour when hitting at 30deg from vertical from 100m distance and 14 mm from 500 m.

Juha