The only time I've ever seen an AI unit enter through an open gate was by accident. And then the units just milled around and did nothing until I killed them. For some reason the AI isn't programmed to take advantage of an open gate. It would certainly make sallying more difficult if they were.

And I don't have a problem with the "luring" tactic so much, that is semi-valid. The problem is when the army rushes forward and just stands there. I haven't sallied, so there is nothing for them to attack. They should recognize that if a tower is hitting them, and they have no valid targets, that they should move.

Bh