(using the newest darthmod stuff, os18)
There is a problem with the hard to breach gates of castles/cities.

What happens is that the enemy usually only uses ram + ladder + tower, so besides having to block the ladder/tower you are free to stack archers on the walls... and the problem is that because of the LOOONG time
it takes to batter it down your archers can kill so many enemy units that it is unbalancing...

on an average battle (and I played over a dozen) my peasnt archers (weakest archer unit) would score about 250-300 kills per battle (using large units - this means about 3x its own number of men); now these kills wouldnt be on other peasnt (any type) but on spearmen, merc. spearmen, dis. feud. knights, dis. chiv. knights, mailed knights... etc. etc.

this causes me to win defensive battles that should in no way be won - I have 2 units of dis. feu. knights and 2 units of peasy archers, thats 400 men total. I get besieged by 1000 knights (dismounted feu, chiv, mailed, feudal)...
200 of the enemies knights die on the castle walls, about 600 die before the gate is breached from archer fire and finally the remaining few are made short work of...

simply not cool that peasnt archers are the ultimate unite in the game
(and I am not complaining about their kill rate, they dont kill many knights a volley, but there are so many volleys... )

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suggestions to improve sieges (AI offense)

1) make them use more towers/rams - this will tie up more units on the walls and not allow free archer fire

2) fix the only 1 unit can climb one ladder by AI (or ram)

3) make the gates easier to breach
a/ so that half the enemy army isnt killed by a single archer unit on the wall
b/ so that gates / tower / ladder attack is coordinated in time

ad. 3/b
right now, it takes about 5 minutes AFTER the ladder/tower starts to fight for the gates to be breached

this means that by the time the enemy troops enter the town, the ones on the walls were LONG been massacred... and since there is no follow up (because of the bug) it means that the defender can first use all his units on the walls and then slowly walk them down to defend the gate afterwards

the point of the ladders/towers is to force the enemy to "waste" units on the walls at the time when they should be defending breaches

this would really help the AI a lot, cause right now it is way to easy to hold any half decent and half manned fortification (opposed to conquering it, which is much easyer)