It’s entirely possible to have two different sets of behaviour programmed for the AI and apply different behaviour on different tracks.
If the track length combined with the difficulty to overtake is not the explanation for why a different behaviour is used, then what could it be?
I get the first sentence. The question is why. Why have AI be courteous over one long track? Why not the other long circuits(Bathurst, Yamagiwa+, Alsace, Suzuka, etc)? Why not ALL circuits?
I'm currently doing the GT3 RS Endurance races(Suzuka and Dragon Trail). Normally, if I'm racing GT4 cars at Suzuka, the AI shed pace through a host or corners. At Suzuka, the Porsche AI are much quicker. Why is that?
What's more, I'm racing at Dragon trail. For the first 15 laps, The AI are super aggressive. Blocking, filling my mirror and drafting to pass. They've actually passed me(I was shifting at 7000 rpm to conserve. To add, some AI that pitted, are using RS tyres). However, why is it that they are programmed to be that aggressive?
That's actually backwards. Why should it be hard to overtake on a short track? Virtually no chance to win in a short amount of time. The longer courses should be the hardest as it gives you more time to win. An Arcade race at the oval is about 15 laps and around 4 minutes time to win. Arcade at N24 is about 9 minutes. If it were multi-class, I could see the courtesy for slower traffic to move over. If AI are slower in any class, then AI should do thesame.
As I mentioned before, if PD programmed AI at Bathurst, to slow up for 2kms(as you say), they should have added signalling and moving over. Not shave speed on the racing line, to cause collision.
One more thing. In one of the Mazda roadster races at Tsukuba, I posted a pic of an AI flashing it's lights at me, as I was passing it. Did I trigger something? Was I too aggressive? Maybe that was an early test they've left in. Same could be true for the AI at the N24. I don't know.