heh well I went into that a while back as well... and that setup is prob the sillyest thing ive ever seen in my life. I redid all my lines with SS 6AN and billet CnC rails but when I did it I created a loop rather than a split heres a little diagram to explain
Parallel:
0000000000000---(rail1)-----
(car)----<000000000000000>------FPR---return
0000000000000---(rail2)-----
(EDIT: THIS DIAGRAM I CANT GET TO WORK RIGHT PRETEND THERE ARE NO 0's) I can post up my pictures I made when I designed the system but I will have to do so tonight
My setup:
(car)------(rail1)-----(rail2)----FPR----return
with that being put out there and understanding the physics of water flow aka water will take the least path of resistance. So if I split the line prior to getting to the rails im not garenteed im getting the same amount of fuel into 1 rail as the other because the FPR is on the opposite end, as long as it sees the correct pressure in the 1 line after the T from the rails it will say your hunky doory. Whats to say one of my rails/lines wont clog on one side but still produce the correct pressure on the other to read correctly on the FPR (I have a gauge on mine)
with the way I set it up you have 1 flow, 1 route, and the FPR is at the end of this monitoring / creating the pressure it needs in the 1 line. this will garentee im getting the same fuel all the way around. If my FPR senses a drop it will make the corrected compensation and if the single line is clogged well its going to stop the whole bandwagon.
now if you wanted a Paralell setup that would work you would somehow need to make sure that each rail line received the same amount of fuel (this cant be done with just a T line) so you would essentually need like 2-3 FPR's in place to do this. That would add 2-3 faults in your system as well so if any one bit failed and a FPR is a major bit then your SOL. Less faults the better, less splits the better.
Think of it like a drainage system on a house or something say you have pvc pipe under the ground to re route water when you get a heavy rain, you have 1 pipe going to 2 pipes draining in seperate places, if I were to pour water in the single end and then go to each end of the pvc pipe and collect the water that came through would it be 100% identical to the other side? it would not. Simple fluid physics and I think the whole idea of the way people do there fuel is plain silly silly silly. even looking at most aftermarket kits they are done this way as well hence why I made my own kit. Cars been running now sence 2006 so that's almost 6 years of 20+ psi running this setup and ive never had a fuel issue other than keeping 93 in my tank
with that being said, do you have parallel fuel rails?