It sounds like the master is plumbed backwards or something is mis-matched. On the Strange Mopar style unit, the port nearest the pushrod supplies the highest volume of fluid. Typically on a drag car with big tires and larger brakes on the rear, that is where the rears are plumbed to. I would look at the Wilwood calipers and compare the bore size to the Strange units. I've had certain Wilwood calipers with small pistons relative to what Strange and others use. I've had to go to a 7/8 master to make the brakes work with those. I stopped using them, but still have to deal with them sometimes. I also have not needed or used a prop valve in years, once the system is set up correctly.