Adjustable proportioning valve mounting location

My car has a spot under the car on the drivers side where the rear channel runs that had a residual pressure block (my car was disc/drum). I removed it and swapped in the proportioning valve that I have since removed and just put a splice in for Disc/Disc.

If you car doesn't have this then somewhere past the proportioning valve in the line going to the rear. Whatever works best for you.