Psitticine : yes same mechanism in doms I. With the fortified city having the highest admin (50).
Pardon me if I led you to believe that the rules were differents in doms I
In doms I there is a deprecated stat attached to castle, which is the supply bonus. In fact castle give 4x their admin value in the province there are in, and a decreasing bonus further.
How is based supply bonus now? Still tied to admin value?