I got tired of all the nonsense about differentials. So the last time I tuned my Sniper I set the first reg at 180 then started tuning. I ended up with the 2nd reg @ 135 to shoot 27.5 gr slugs. The only difference I saw was my plenum seemed to recover quicker. The first reg has zero affect on the what is downstream of the 2nd reg.
The only purpose it serves is lighten the load on the 2nd reg.
I know a guy who set his first reg @ 200 and his second @ 90. No issues and if he wants to up his second reg to tune for slugs or heavier pellets all he has to do is increase pressure on the 2nd reg. No dumping air to adjust the 1st reg to accomodate.
I am an FX fan boy and admit it with a smile on my face. However, I question the value of the two reg set up.