Parthian Reforms

[seriousbusiness]

I apologise in advance if this is somewhere else but I haven't come across it yet.

I don't understand how the Parni/Parthian reforms work. I'm enjoying them a lot and now have the troops and money to consider the reforms. I've got most ofthe Seleukid East and destroyed Baktria (early, they had only two provinces) and am about to at least weaken (if not destroy) the Saka. I think they'll attack any turn now. Could someone explain it to me?

They're powerful and great value, but it gets a bit old always using Parthian HA's to mow down inf stacks