Not sure this is a coincidence or a fact. My first campaign I played was English and I faced the passive AI many times while fielding archer heavy armies. My second campaign is Milanese, so I field chrossbow heavy armies. So far, I have yet to see the passive AI. On three occasions in which I brought out a crossbow heavy army against no-missile troop AI armies, the AI would make a move towards my army, get stopped by my missiles and then... turn around and retreat to a better location (high up in the mountains or somewhere in the trees)... sounds like a reasonable action on the AI part since I was the attacker. But I never saw that happen when playing archer heavy English armies against the AI. Could it be, that it's only archers that the AI becomes passive against?