A quick question that I've had trouble figuring out just by playing with the game settings.  Is the game setting for 'extreme' planets a subset of the total number of planets, or a subset of the number of habitable planets?

For example, if I want a universe with a large number of radioactive, toxic, or high gravity worlds, and a small number of earth-like worlds, I would clearly set 'extreme planets' to its highest setting, but would I want 'habitable' to be set high or low?  If extreme is a subset of habitable, then I would want it high (lots of habitable worlds, but most of them extreme).  If extreme is a subset of total planets, I would want habitable low (lots of extreme worlds, few habitable worlds).

Does anyone know how the engine works for these settings when it generates the map?  If not, any suggestions on a fast way of testing this?