From what I can see from videos, I have figured this out. If you hit on the first hit, the second is half of the first, the third is half of the second, rounded down, and the fourth is the third + 1. If you miss on the first hit, but hit the second, the third is half of the second, rounded down, and the fourth is the third + 1. I havn't seen enough of hits where you miss the first 2 or 3 hits but hit the third or fourth to determine anything about their characteristics.