This has been noted before, and it seemed to be unique amongst just certain AIs. But as I've done some testing, I've also only been noticing it on larger maps.
For example, i've been playing an Immense Rare Habitables. And the Drengin never colonized anything outside of Drengia. And I couldn't figure out why, until I played a Tiny map against the Yor.
The Tiny Map was on Suicidal, and I was just testing some stuff out, so i sat on my HW system. The Yor very quickly sent out colony ships but then...never once crossed my influence border. There was a good 20 planets in my sphere of influence, but they never even made a move for them...well, that is until their influence started growing and then they started colonizing planets closest to their worlds, to minimize culture flipping
And on an Immense map, there are no more stars than in a Gigantic map (they are just space farther apart). The issue with this is that the AI lacks the ability to 'reach' out, especially if not playing All Abundant to spread out. This is why so many see the Korath building Influence starbases early on. They're trying to get it where they can actually grow, but since the AI won't colonize in another sphere of influence, at least early on, they are essentially getting suffocated to death.
