Some admission is probably in place here, but the reformed Parthian "boundaries" are somewhat static and not nearly as refined as Hayasdan's process, and this is mostly due to how the Pahlava start out as nomads. The problems that later arise pertains mostly to areas just outside of the boundaries, lands into India, Bactria, Soghdia, the Caucasus and Cappadocia, and basically the origins of Arsacid power, at Dahyu Daha, Margiana and Chorasmia. They are restricted to pastoralism which ultimately leads to low-level fortifications at best and limited economical means. Just a bit awkward, but that's how the system looks like...

The reforms are not mine; I don't do any coding, and the concept itself as an idea (Which is undeniably more realistic, in spite of its short-comings) is a product of Teleklos' and Steppe_Merc's design. I really can't take any credit for it (In my own small modification, I have extended the area of the reforms slightly to match Bactria, Margiana, Paropamisos/Kophen and the Caucasus, nothing overtly crazy or irrational).