Herefordshire is the seat of the region. I like capitals that share the same name as a region - its one less name I have to make up .
The Distance between it and its 4 closest neighbors in the surviving town map is approximately 12 miles (See circle in Picture). This, I have been told, is a common distance between European cities because (I am told) it is comfortable for horse travel.
So be it. 12 miles between larger villages\cities etc... Less space and they are probably competing for resources and influence. More space hampers communication and trade. Without a rich resource or an exceptional element two cities inside of 12 miles are both going to be smaller or on a collision course.
Herefordshire is also on a river. But only 2 of the 8 surviving towns are on rivers. Notably none of the towns are on the coast. (This was a frontline between Norse and English for a while.) I can imagine that the bonuses of more trade might be necessary to achieve higher town sizes (and bring in more food) but they increase the ease of travel for invaders as well.
Wikipedia gives me this....
Herefordshire has always been esteemed an exceptionally rich agricultural area, the manufactures being unimportant, with the sole exception of the woollen and the cloth trade which flourished soon after the Conquest. Iron was worked in Wormelow hundred in Roman times, and the Domesday Survey mentions iron workers in Marcle. At the time of Henry VIII the towns had become much impoverished, and Elizabeth in order to encourage local industries, insisted on her subjects wearing English-made caps from the factory of Hereford. Hops were grown in the county soon after their introduction into England in 1524. In 1580 and again in 1637 the county was severely visited by the plague, but in the 17th century it had a flourishing timber trade, and was also noted for its orchards and cider.
http://en.wikipedia.org/wiki/History_of_Herefordshire
So I am going to assume that these town placements are largely agrarian - farms and such. Especially in the middle ages large populations need their food producing regions to support their higher population. Only for the system to work the food producing regions have to export their people along with their food or they'd have nothing to sell .
Sigurd
So this is the running rule of thumb -
Small to Medium Territory
40ml diameter
1 major river
Good farms and lands but no exceptional industry.
2 Larger cities - probably one dominant keep\castle.
Influence\support radius around larger cities 12ml.
6 Villages
As many as 16 further sites of interest, ruins, failed cities, manors etc..... (this is only a rule of thumb.)
I can't say this is historically researched but I'm content that its vaguely plausible based on this very small sample.