One point in favor of the more dynamic fights around sieges is for people with lower tier computers to be able to effect those fights without having to directly engage in them.
On the zone around settlements during sieges. Some villages are quite a distance away. Sometimes putting a small ring around a village in addition to the ring around the main settlement might be a better option.
If the ring of improved influence/rep/ faction and relational rep is completed. Finding a way to set it over the caravan as it travels to the army might create an easy solution to weight fighting against or near the caravan. Possibly creating epic running battles on the way into a contested zone around a siege. This would help pull captains away from the area around a siege where bonuses are active and have fights begin around the caravan.
I expect ( I do not have data but my reason suggests) that the supply caravans+ contested zone might help factions that are down. Especially if/ when a faction can not form a army big enough to oppose the enemy faction. If the forces of a faction is indeed depleted, the factions forces become weighted instead of combining to fight separately around sieges and become extra aggressive about picking off supply caravans.
While there may be missions from Army commanders to go out and collect food currently. Sending out part of there current force to act as a screen while sieging to contest the area around the settlement and to collect more food to sustain the army. Personally I like to use high end units. Players with high end units would make excellent area denial units and also be good at gathering more food for the army.
A mission or set of directives while a siege is underway could make the situation around sieges much more dynamic. Especially with the call back mechanic.
Impact of a caravan loss on moral. If a caravan suppose to feed an army is lost the army is likely to lose cohesion and moral. Opposing this the successful arrival of a caravan could boost both cohesion and moral. This could mean that the arrival of a caravan could peak moral and cohesion in an army leading to that being the best time to assault the walls. Opposing this taking out a caravan could become the straw that broke the camels back and break up and army in the field.
Thanks again for your time. It would be beyond awesome to see this in game.