So I was testing with planet quality in a custom home system I built to test large planet quality numbers to see what would happen. I did this until something interesting happened, using the Kryseth system as a base I built a three habitable planet system with the homeworld set at 60 the two other planets set at 20. The 60 planet was never sixty I have tested this around 12 times and it seemed to be a random number between 60 and 40 that it was set to although the class 20s never changed. The next thing I will try is to find the start of the randomization in planet classes. As well the sixty class planet could not be terraformed except with a biosphere or alternative improvement. I will try to find this number and put it in this post before I post it.
I have experimented and my results are inconclusive, I do not know.
However, it appears that it will start to vary above 43 but is much more stable, than higher numbers. If it does start varying the planet class you put it, for example 60 is how high it will go, it never goes above 60.
Hopefully someone can understand why it does this, I can't.
Oh, and one last thing,
Cheers!
-Jeff26jeff