Well here it goes:

I am wanting to use the Knights URX 2 rail and the standard carbine length piston conversion kit.  Just for some background information, this will be my 3rd Adams Arms piston build, but first venture into an outside of a "verified/approved" rail system you have on your website.  I have previously used your Samson and Daniel Defense Lite rails on previous builds.    

Anyways, the rail I am wanting to use on this build is the Knight's Armament URX 2(in carbine length/7").  When assembled, the piston/op rod seems to fit fine, but when I add the "drive rod bushing" to the piston/op rod assembly, the piston/op rod assembly sticks out from the gas block approximately 1/4"(I might add with "significant" tension, as the piston spring is being compressed at this point).  It appears as though that if the "Drive Rod Bushing" is eliminated from the set up, the piston/op rod assembly fits perfectly.

This now brings me to my question which is, "Is the Drive Rod Bushing, that is included in the conversion kit, for support of the piston assembly, or rather to absorb some of the recoil of the system?"  

In my mock up, it would seem that if the "Drive Rod Bushing" were to be eliminated from the set up, the piston assembly will fit fine.  

Also in addition, the URX 2 does seem to "support" the piston/op rod assembly by roughly 1.25" before the piston enters in to the upper receiver.  

I hope that was clearly explained as I know sometimes trying to type out the situation can be somewhat unclear at times.

ETA:  I also did email this question to Adams Arms, but am wondering if anyone else here may have some first hand experience/knowledge.