Dan - I just observe the amount of "polish" for lack of a better word, on the front rotors as opposed to the rear rotors. If there were more bias on the rear, the car would get a little squirley when hard braking is done. When I had a bias valve on a car, I would find that loose spot and back off the adjustment to put just a little more bias on the front, until I was happy with the braking. To me, this made the vehicle stop shorter and the braking to "feel" much better. This may not be the way others do it, but it is the way I used to do it. A GM or other American car mechanic could tell you how the dealerships adjusted the proportioning valve. That I don't know but would like to know.

Jim