Aginst AI I sucesfully use tactic where i put at leaast three melee units behind gate forming empty square with one side being gate. (I know, nothing new.)
Sometimes i've seen enemy run through gate and panic without countact.
But this works becose AI in general sieges stupid way - does not try to flank with towers/ladders, so player can concentrate his defense on one side and dont bother with rest.
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