I have a Bourget Kruzer FXR that has a single 6 piston Jay brake rear caliper and an 11.5in rotor. The rear brake is weak and the pedal feels rock hard. It takes way more pressure then it should. I have flushed and bleed the lines. I am running EBC HH pads with a EBC stainless floating rotor. I got to investigating why and it looks like it has a 3/4in bore rear master cylinder. It seems like the master Cylinder is just to big for a single rotor. I'm guessing that i need to go with a 5/8 bore MC?

So my question is what is the recommended rear master cylinder bore size for a single J6 caliper?