A RV doesn't give you any more rear brake power.... A residual valve doesn't add more braking to the rear it helps to keep the piston from being able to retract, and keeps the pads just barely against the rotor so it's not taking up all the slack.... exactly like how a not adjusted properly drum brake is when the adjusters don't adjust is EXACTLY what you have all the time at the rear and the reason you have the rear pads in the back still after going thru 2 sets of front pads, when you hit the brakes you only get so much travel and so much fluid to work the pistons in the caliper, and this is why you have changed front pads twice and rear brakes 0, a normal car should be getting rear brakes just before the fronts need the second change, not 2 and keep on going, that means the rears aren't doing 40% of the work, not even 20% of the work.
A residual valve is not a prop valve, it will never make more psi at the rear, it will simply hold the pads against the rotor and take up the slack the fluid won't have to and actually put 40% of the braking on the rear, which is why your front pads are out twice and the rears are still fine.
