Wilf...assolutely incredible how you can get right to the essential point, but I do wonder about one thing...
What else is she wearing?
The Big Gasbag!
P.S. While I am not a professional mechanic, I know better than to stay at a Holiday Inn. I believe the essential reason for the front needing the bigger master is as Wilf points out...matching components. Bigger brake swept area, pistons, etc. need a greater volume of fluid. The front better have the bigger brakes! A properly functioning master will yield the pressure needed.
If we were to follow the smaller hole-higher pressure analogy, then as brakes get bigger and more pistons are added, we should drop down to...say...1/8? Piss on that...wait, yeah, that's the ticket...
