As per title really, it confuses me that Ravenna is right on the edge of the WRE territorially, and as a result is rather vulnerable, plus, being at the top end of the Adriatic Sea, trying to go from Ravenna to anywhere else by sea is delayed by the great big ol' boot of Italy.
So whilst a Military capital is probably best suited to being on the border, what if the major peacetime capital was a massively rebuilt Carthage, or somewhere else in Africa.
It is centrally placed in the Empire, with the arguable exception Gaul, which would have the Military capital anyway.
Or was Ravenna being on the border a crucial reason it WAS such a useful capital for the WRE?