IDK if its that simple. I've seen a T-34/85 take at least 5 rockets to the side with no effect (was sitting next to the guy). When he pulled forward, there was a cluster of craters, a clear spot (where he was sitting, and blocked the rockets), and then another cluster of craters.
I've also scored hits on panzers yield no kill, which makes me think theres more than "it penetrates 90mm of armor, so if you hit something that has less than 90mm's of armor, you kill it".