Because they come in on the wrong side of the castle, and get stuck behind mountains. Thus causing my defeat.

Can't really ask for a fix but... it still sucks when that happens. And I don't wanna hear "Oh that's realistic!" cause it's not, cause if the AI was allowed to go behind the "retreat" line, they could easily go around to a path that leads upwards. They just happen to get stuck at this one point where it's impossible to find a way up.

Woulda won too. ing pathfinding AI...