Adding special resources to custom planets

I was messing around with the customPlanets.xml file in TA and I was wondering, is there a way to add special resource tiles to custom planets or at least increase the chance that they will appear?

I created a system of 5 planets all ranging in PQ fro 16 - 22 and all had a moon.  Not a single industry special tile on the planets.  A few had some of the other tiles.

Does the AI determine the placement of special resources throughout the galaxy based on some sort of balance?