In real life IL2s were practically impossible to take down with fire from pure 6 o'clock. Finnish pilots always attacked them from a slight angle: above -> pilot and engine, both sides -> wingroots(thinner armor and fuel tanks), below -> engine and radiator. Afaik wingroots and radiator were preferred as targets.
Ingame they go down a bit easier. My favourite is the wingroots from above, since that way you usually take the whole wing off. Works even with "teh porked" .50 cals.
The engine is also pretty vulnerable to .50 cal fire from above.