Proportioning valve / rear brake problems

It appears to me that you have plumbed it in reverse. The chamber closest to the firewall should be plumbed to the front brake system. If I am correct about the reversal, you need to correct this.The rearmost part of the valve inside the master is directly coupled to the brake pedal, whereas the part that is designed to activate the rear brakes( which is the forwardmost chamber) is hydraulically coupled. It may be confusing, but the rear chamber is the front, and the front chamber is the rear.
Your brakes will work either way it is plumbed on the inlet side of the P valve. But if you have a failure in one end of the system, that's when the problem arises.You really want the front brakes directly coupled to the pedal.The fronts do 70 to 85 percent of the work, on most cars. The rear usually fails first.
Depending on what's going on on the outlet side of your P-valve, you may be proportioning the front brakes. The ports on the valve are coded. You will see FI,RI,FO,and RO. F is front, R is Rear, I is Inlet and O is outlet.If you cannot see the coding; the switch-end is for the front brakes. The topside are inlets, and the bottomside are outlets. The knobside is the top.