If you decide not to go with my hatching suggestion, you might want to try placing the troop circles in the disputed/shared regions on the colour boundary. This might make it more apparent that the region falls into both zones. This looks very feasible in all cases except S.-H. which is a little cramped, unless you shift the colour boundary instead of the troop circle. Of course, with my hatching scheme, the boundary is diffused and the troop circle looks shared no matter where it sits.
Another reason to try my scheme is that it might avoid confusion about boundaries. For example, with the current colouring, Venezia, Lombaria, and Custoza almost look like four territories with one of those confusing four-corner boundaries. Yes, your hatching runs through all of Venezia, but my eye takes more note of the sharp colour boundary, leaving me wondering at first if Venezia can even attack Custoza.
Is there a typo in the legend? Is it not supposed to be "Pr
eussische" (sorry, don't know the code for the German sharp s)? Also the colour of the PPR box does not match the map very well: it seems too white.