If de-linking the brakes the rear master cylinder should also be resized.
We debated the front-rear setup a couple of weeks ago. I will look at the sizes I used on my bike with duel brembo gold series on the front and single caliper on the rear. I am happy with the master cylinder set up. I can adjust the compression setting to slow and nearly do a two finger stoppy. I can easily slide the front end. The rear tire will lock up with a moderate amount of pressure.
Prior do de-linking the brakes, I removed the front left caliper and place a paint stirring stick between the pads and hung the caliper safely from the bike. I then rode around on my drive way and found that the rear brakes offered no stopping power and only dragged on the rotor. I considered them to be useless. The pads are HH, the calipers clean and functional and the swingarm control valve adjusted. I found that to get the maximum stopping out of my bike at that time, I had to use both the front brake lever and the rear brake lever to use both front brake calipers.
I am a on the brakes or on the throttle kind of rider. Long rides at a steady speed bore me. I ride for entertainment and not as a form of transportation from home to work or the grocery store. Every road is a potential race track. I can go from 0-60-0 on my driveway, it is down hill and around a curve once I pull out onto the road either direction. You can tell it is riding season by the single track black marks on my driveway. Some continuous from the garage to the street.
