rear pressure low in system HELP

Yesterday I by-passed the adjustable valve and there is a big improvement but, I don't feel it is right. The car is on stands. The rear brakes are more effective but, will not lock up. They slow down, than stop. It is easy to move the rear wheel with a bit of gas peddle.

Might this be a factor:

I have 3/16" brake line from the master cylinder to the coupler (adjustable valve now by-passed) then 6" of AN 4 ( 1/4") line to a firewall bulk head fitting. From the fire wall to the "T" on the differential I have AN 3 (3/16"). From the "T" to each rear disck brake caliper is AN 4 (1/4"). Maybe it's a volume issue & not a pressure issue?????

My understanding is that hydrolic pressure is equil in all directions. I wonter if going 3/16" to 1/4" to 3/16" and finaly 1/4" is having some sort of restriction/expansion effect?