How does this work?
In my current game I put the settings at 1 NPR, 30% NPR generation, with precursors turned off. So far I have discovered 32 systems, 27 of which have no NPRs, and I know the other 5 have no NPR planets, because there are no habitable planets. I think the original NPR has had two small combats. I'm in year 2051. I assumed turning off precursors increased the chances of other aliens, but since I've not found anything, now I wonder if the game just generates no aliens if precursors are rolled, decreasing the overall chance of aliens. I'm using 4.91.