Has anyone put up a custom arena, gotten a friend to help, so you can drive a jeep up to a parked Yak3 and counted the number of rounds to destroy the Yak3? Add in a K4 and a 47M as controls.
From my offline testing, the Yak3 seems to have a very tiny area to land hits against along with the appearance at random times of being tougher than a Jug against 20 and 30mm ammo. The Brewster has the tiny hit area but, responds about how you think it should to damage. The K4 seems to have a lot of armor plating compared to other 109 taking more rounds to knock down. FW's oil hit first, then burn second more often than loosing big parts. And bombers now uniformly take a lot of 30mm to break them apart.
Thinking that the Yak3 may be a newer damage modeling because of the generation of it's 3D modeling. I tested it, the HurriII and the new Ki61 offline in the beta. The Yak3 in AH2 or the beta responds with the same randomness and need to aim precisely. The HurriII does seem to require better aim along with the new Ki61 but, they both responded to damage more like you would expect.
At 200 the Yak3 had more episodes of needing a second 30mm than the other Yaks. But, on some days of testing with single 30mm rounds from the K4, all test subjects at 200 go boom from a single round into the lower rear fuselage. Then on some days the Yak3 defies the 30mm to destroy it with a single hit. There is your random factor I cannot explain and have asked others if they could perform similar offline testing with a K4, single round shooting at the Yak3 into the rear fuselage.
An interesting side note about the Yak3 damage. I noticed of the yaks it more often would part with the horizontal elevator appendage than the others to a 30mm while the others would more often be destroyed. This is why several players testing the damage modeling independently would make for better feedback.