I was a freelancer in a some lords party when we took on 100+ prisoners and shot to 250+. They slowly deserted until his party was back to it's more normal figures, around 175. I assume this happens with those super huge parties as well.
If you were looking to tweak the prisoners thing, I would tie the prisoner quality to the size of the bandit party. Afterall, a player typically expends some of his own troops defeating that enemy party, therefore some rewards are in order. For example, say it is one of those bandit leader parties of 150-200 bandits. Once defeated perhaps they can offer certain level 5,6,7 troops for hire. If it were a more typical party, perhaps offering up level 3-4 troops would be nice. It sort of works logically as well, since the bandits would keep only the most valuable units for ransom and only the larger parties ought to have higher tier units captured, due to the difficulty in doing such.
Of course, the bandits obviously hold caravan or manhunter prisoners typically, so maybe just coding them to spawn with certain units is an option? I have no idea how the coding works....
