Agreed , ai is really quirky about where they send their ships. I had a game where Black holes were set to be fairly rare and I had only one in all my space.
3 different empires sent all their trash ships there and just parked for rest of game til I got sick of it and killed them all. Tried to pretend they were all trapped in the gravitational pull to make it seem logical and add to the fun but they just kept coming like I was handing out credits. Was weird, once I killed them all the word got out and no one ever came back.
Hope when they address this I can also have borders that actually stop ships from crossing. Would be nice if like in star trek you knew better than to fly into enemy space for fear of starting a war. In this they do it and then mock you in diplomacy saying how you should just have open borders since they don't respect yours. Ideally, I would like to be able to destroy any ship in my space (providing we don't have open border pact) without going to war.