I don't know this for sure, it's only an educated guess... but I think the AI will demand surrender when they're 10x their enemy's size (which also happens to be the size humans have to be to get an AI to surrender to them, which is where I get the educated guess
). If you're trying to help the AI along, I would say go in and kill all the ships of the smaller AI, since ships are a large part of the score. You could also try building a bunch of big ships with no non-essential components and giving them to the bigger AI as a gift.