You can bust Panzers by either diving down on them and piercing their top armor. Or, like it was done in the real world (and much easier) attack them straight & level from behind and shoot at ranges close as possible, best around D200
Works both with Hurri D and Il 2
For Fireflies,you have to attack the top armor, preferably over engine. Even Il2 still can take the shermans engine out, if you can hit the grill.
I have never managed to hurt T34 & Tiger with Il2 cannons, but I now do regulary pop both in Hurri 2D. You can practice those attacks offline. Especially vs Tiger angle must be as steep as possible.