This seems to constrain offensive axes of advance, and also defensive lines, to a tremendous degree. For example, are Germans in Cassel and Nuremburg really out of supply and at risk of dying? Seems unreasonable.
Yes, it constrains axes of advance and defense in historically accurate ways. WWI was famous for that!
Were there ANY significant military actions near Cassel or Nurmeburg during the real war? No. Should there be in the game? No. By comparison, Monticello Virginia is a wonderful place, but could it sustain 100,000 armed men - and 25,000 horses - at a moment's notice? No. It might take some time and preparation (infrastructure) to enable that. So if you must have a fight in central Germany, then spend a few points on infrastructure to enable that.