Russian airplane in general take a lot more ammo to kill. I am saying this from flying the ki43 and shooting airplanes in the same place (wing root). Spits, wings come off very easy. Jugs, mustangs... easy. German airplanes... easy. Russian airplanes, most of the ammo load.
I have no doubt in my mind that the damage model HTC uses for the airplanes is accurate, I understand Russian airplane to have been built a little more ruggedly then other nations.
So when flying against Russian airplanes, I just aim for the cockpit. The yak3 reminds me of fighting a spiteen.