Okay, I get how the system works. But from what you say, the system is not dynamic. It provides pressure to the rears that is linearly related to the pressure to the fronts. If you add weight to the rear of the car, both will squeeze harder because it will take more friction to stop the heavier vehicle. However, no tire is running out of traction in this case. I really do get your arguments, I'm just saying that weight will not make a difference in a normal stop. The rears cannot do a different percentage of the work with a different weight balance unless you change the braking system. If you do shift the weight rearward when designing/modding a car, it makes sense to let the rears do more by giving them more pressure, but I can't see how you could change the relative amount of work done by the rear brakes unless you put more pressure to them.
