Not too long ago I was flying a Mosquito when I came across a friendly Lanc with engines out and under attack by an enemy La-7. I dove down, quickly lined up the shot and fired cannon only. Two rounds (at least) hit the Lanc and I heard two crunch noises (I have wood impact sounds for the Mossie getting hit). Nothing on my Mossie was damaged.
I strongly doubt there is a damage multiplier on KS. I suspect that it simply applies whatever would have happened to the target to the shooter instead. A Lanc being a big, tough bird can take two 20mm Hispano rounds with nothing breaking, thus I lived. If it had been an A6M2 I would probably have got the good old "instant trip back to the tower".
BTW, the La-7 exploded outright from the large number of Hispano rounds that slammed into him.