All of them kind of work the same way except Picket at the moment. Picket ships orbit their target at a fixed range, everything else just goes to a fixed range and tries to stay within that range of its target. Mostly it's just a matter of roughly how close you want the ship to be to its target plus which modifiers you want on it.

That said, we're probably going to make some changes as it hasn't been revised in a long time and it's now quite out of alignment with vanilla.

You can see the values in 01_standard_ship_behaviors.txt

Ah I was wondering about this. Had some ships in a game yesterday just sit there outside of the range of their own beams, but evidently in range of the enemies, and just get slaughtered trying to kill things with just their torpedoes.

Any recommended AI computers for the various ship types? As what I thought was the one the auto-build defaults to was the intended role of the ship (like light cruisers being pickets) as otherwise I might just put them all onto intercept. Even if sometimes destroyers just decide to hang back for no reason anyway, lazy gitz.

Yeah, the main things that distinguish them are how the ship decides what range it wants to be at from it's target, and how to get there.

It's pretty similar to vanilla - for most it's the "median" range of their weapons, excepting Engage which is "min" range and Artillery/Carrier which are "max" range.

So basically just don't use Artillery or Carrier unless you really want the ship to try to stay as far away as it can, while still contributing a bit with it's longest range weapons.

Intercept, Line and Picket should all be pretty sensible, and look reasonably pleasing, for most ships.

Oh and sometimes, yes... ships just appear to completely ignore the behaviour and do crazy things. Most of the time it's because they have switched target, I think, so they move to get range on a new enemy. If anyone has great expertise on Stellaris ship combat behaviour feel free to share!