AI Resignation script

Okay, so I heard somewhere that that AI will resign if all of their TC's are destroyed and they have fewer than 4 vills left alive.

However, a game I played today disproves that entirely. I went up against a "Hardest" AI, and the AI eventually resigned after 2 hrs of being constantly rushed and pinned down.

However, he had more than 20 vills left, as well as 2 TC's and a Castle.

So, what's going on? Is the resign script different for each level of difficulty in the AI?

Is there a way to remove this script somehow? I admit to being a bit disappointed when I roll my troops into the enemy base, and after only destroying 3 military buildings, and shooting most of his army with mass archers - he resigns rather than fights to the death.