Is there any 'method' for determinining what type of planet you are likely to get from a genesis torpedo?

I have used 8 genesis torpedoes so far in my game and 5 have been M's and 3 have been H's. I used the torpedoes 3 times over either a SSS or BBB port, and 3 separate times in dead-end sectors. I find this really odd because I thought I would that with 8, I would have at LEAST 3 different planet classes. I would really really like an O.