What about giving Heroes the ability to set retreat percentage to 100%, and giving them a flat bonus to whatever value makes troops break (morale?)?
I can see Heroes inspiring their men to fight to the death more frequently.
I like both these ideas.
For the retreat % that is tied to the character's leadership skill right? So maybe just a flat bonus to the max percentage they can set. I would still want it connected to their leadership skill at least somewhat, rather than letting a hero with hardly any leadership skill be able to command his troops to fight to the death.