Just for fun, I decided to try playing around with the custom map feature a little. I have to explore each map "by hand", rather than just looking at the generated result.
My first game I created a 10 planet per star with 2 star systems (and only one other AI). The result I expected was two more-or-less equal systems, with the AI in one and myself in another. What I go, was one system with 10 planets, both me and the AI, and a second system with 4 planets (planets being any grav well, asteroid or planet).
This next one, I made one star with 100 planets (I didn't count to see if I got all of them) but the placement of one of them was... odd. It was a Terran planet, just about touching the local star. Not the star's grave well; the star itself.