So I noticed while observing ai defend sieges the attack ai will attack the town and while the defending ai will have some armies outside the siege wait until the attack ai is weak enough to charge into. This only happens with ai though and not players, giving the player a overwhelming advantage when it comes to sieges. A while back someone introduced a ai reinforment mod which is gone now but was a great addition to the game. All im saying is having ai reinforcement help defend(if they are in the vicinity) the siege while a player attacks after a certain amount of time has passed would be a good feature. Time in the campaign map should not stop when a player is in battle just like the ai when they fight. It will make the game more dynamic since you do not know who will join in the field fight.