I think, if distance from capital could be modified in a way, that, for instance, half of problems come from absolute distance from capital, and the other half would be related to distance from duchy center, that could eventually be one simple step to give more sense to duchy topography, region joining certain duchies would have more meaning, and there would be somewhat more game about it.
Yes, that would give slight relief to larger realms, but why not, if power of the realm is to much extent measured by number of duchies why cities would not contribute to realm stability that way.
