There is some confusion here but I thought that I was clear. Maybe I wasn't.
The common belief I've read and heard is that the front takes on the majority of the braking and numbers between 60/40 and 70/30 have been tossed around. In between that is 66/34. Do the math.....that is a 2 to 1 ratio. The front number is double the rear.
The theory caries over to caliper sizing. The front caliper surface area is suggested to be approximately double the sizing of the rear.
With the 12" setup, the caliper surface area was 3.3 times the size of the rear.
With the 13" setup, the caliper sizing is just over 2 to 1.