Enemy constellations are specific to a map seed and determine the weighting of enemy spawns. The below graphic summarizes the different constellations and their chance to spawn on every mission type.
MΞRCI for the graphics
https://steamcommunity.com/sharedfiles/filedetails/?id=3214541157
https://www.youtube.com/watch?v=7TM7pHVREUw?noembed