Well there's also this bit from the Gameplay constants:
I'm strongly inclined to think that the "Threat Level" is a global thing, and does not vary depending on whose looking at it, or who they are attacking. First of all, that would be a very silly game design decision IMO.
And second of all, I made 2 player map with galaxy forge, one side had 13 planets each with trade ports, the other side had 1 planet with a trade port. With pirate base in the middle. I loaded up the map from both sides. And the threat level right at the start of the game was "Elevated" against both teams. That is the third threat level, which means it has passed "raidStrengthThreshold:2". Since there were 15 ownded planets, all of which had trade ports... this suggests that the translation from this:
into an actual raidstrength to be compared witht he threshold table is not simple arithmetic, there are other processes going on. I think discovering those processes is going to be very difficult, unless we get help from the people who made them.
I'm willing to call this case closed, satisfied with the knowledge that raid strength is primairly determined globally by primariy by planets owned, secondarily but # of cargo ships, and tertiarily by bounty.
Given pirate behavior, and their fetish for getting stronger when there are more trade ships, it seems like Pirates are best used to harass people who are relying heavily on trade. Could be very useful.... but to understand how useful, or how to make them most useful, we have to understand precisely how trade works, and exactly what trade ships are doing, and what happens when they get blown up...
moving on to that thread.
The next step is revisiting how to predict pirate raid targets.