Is auto calc better? If you don't have any artillery maybe, but with one or two artillery pieces, a bunch of archers and heavy cav even larger more powerful armies can be slain if you do it yourself. The dumb as a brick AI will always stick their cav and infantry next the the big hole you blow in the wall and leave archers in the town square. They refuse to engage the archers that are killing them from 2ft outside the big hole in the wall. Once they all die blow another hole in the wall and any remaining infantry and cav will wander to the new hole. Kill all these, leaving their archer to be mopped up by your heavy cav.