White Lion 说:
Sturgians are able to fight better near their homes, but get rekt when they're in enemy territory
Why tf would Sturgians get rekt in enemy territory? Are you saying all factions should be weak in enemy territory or only Sturgians? If you only talk about Sturgians then in my opinion thats a very bad idea cause it will make the faction weak af and nobody will use it, if however what you're trying to say is that every faction should have a bonus in their own land that's not a bad idea. But I don't agree that Sturgians should get rekt in enemy territory.
I think the question was more general. In the medieval times, with the exceptions of nomads who had their own disadvantages, Any army would fare poorly if far from home. Especially if it was badly or not supplied and had to live of the countryside (read: pillage for food). Creating supply lines in medieval times was difficult at best and morale deteriorates the longer and the further the army is away. Generally people fight harder to defend their own homes than to take a castle from a random baron for a random baron that just so happened to levy you but really doesn't care and will probably discard you and the army as soon as he's in power.
I'm not sure if Sturgians would be especially hampered because I don't know much about Russia.