AI gets any bonuses you like, many of them we don't know, i believe.. Recently, i found one more: spawning FMs: i fight a battle, killed the general, and in next turn that same AI army gets a new one. After that, my assassin killed him, in next turn AI army gets new FM... I assassinated about 4 times, and every time new FM appears. Then my assassin was killed by bodyguards, and i was happy about it: why to upkeep an assassin and kill AI generals when its pointless to do that?