Pad knock back is the PISTON RETRACTING into the caliper when the pressure is released.
The seals are normally(but not always) SQUARE cut so that they pull the piston back into the caliper when the brake pedal is released, only a fraction but can clearly be seen.
If you remove the caliper or disc and get someone to very gently push the brake pedal about 2" then release slowly you will see the pistons retract slightly, this is so that they are not in constant contact with the disc.
If there is defo constant rubbing it depends on HOW MUCH ?, you should certainly be able to easily turn the wheel by hand, it is rare for discs to be 100% true so they will have DTV(high spots) that rub each time the disc with this passes the pads, this is normal.
Can you easily turn the discs by hand ?
The BLACK pads you have are NOT really road pads they are sprint/hill climb pads, and as such will be exceptionally abrasive having to work at very low temperatures.
Look on Rally DEsign webbie for more road orientated pads.
tabetha