Even more relevant: Makers of Ancient Strategy - From the Persian Wars to the Fall of Rome. Also fairly recent, from 2010.
Here the important chapter is the 10th. Holding the Line - Frontier Defense and the Later Roman Empire. This is exactly the time and place OPs question refer to.
Reading a bit into that it seems it takes a more practical then theoretical view on this. For example it notes that foreign relations and military politics many times weren't stood on the rationality or realpolitik, but was subjected to the daily politics of Rome, and military actions were committed or military investments were spent simply as a justification of heavy taxation, or as publicity stunt.