Has anyone figured out how refineries work?  I have noticed that if you put multiple refineries over a planet that you get more crystal and metal income.  However, it seems as if certain planets like Ice planets and Volcanic planets gives better refinery income than other planets.  How can you tell how much resource income a planet will give you with refineries so I can figure out where the best place to place them.  Is there some type of mathematical formula you can use to estimate the amount of crystal/metal resources you can get from a planet?