Hope you can read Japanese. The disk type has to do with the spacing for big brake kits. This picture might help out a little. Basically you'd pick a "O" disk for the rear to get the max size lip. You'd pick a "R" disk to get max brake clearance and the least amount of lip. "A" disk is somewhere in between.
From what I know, the disc designation "A" / "O" / "R" is in regard to the amount of center piece contour. I recently ordered "R" disc and the lip is still wide but the spokes are contoured more and give a greater brake clearance. The flange that the center attaches to is only a few mm different between the different faces. It is a combination of disc face and rim width that creates "Lip".