I believe pirates won't bother your colonies if they're size 3, but don't quote me on that. I just went a long time without...basically anyone in the Sector acknowledging my faction's existence, but as soon as those colonies grew...
I got the raid warning before the Spaceports of my new colonies were finished. Therefore, size 3. I promptly reloaded the game to put new colonies elsewhere (because I have no intention of destroying the established pirate bases if it means they respawn closer to my main colonies by luck).
One thing to point out is that the pirate base always spawns with -1/10%, level 2 and 3 is them growing up by being left alone. As for the early pirate raid, that's actually strange. Are they targeting other factions in the same system as yours?
They were targeting some of the core worlds, but there are no factions in fringe worlds. I built two new colonies in a system with a gate, with pirate bases in multiple nearby systems. I got a raid warning a few days after I started building colonies, before the spaceports were finished.
I do not care about new pirate bases growing up. I want to know if extra pirate bases still spawn at all near fringe player colonies. So far, none of those extra pirate bases that spawned in previous releases have in my current game. None of my colonies suffered pirate activity at all in my current game, and I like to keep it that way.