I'm wondering if it was a formal calculation tied in with wanting to load the front brakes slightly ahead of the rears? Just seems to me that for a given pedal movement/pressure with 3/16" line to the fronts and 1/4" line to the rears, the pressure is going to increase just a tiny bit earlier in the fronts than the rears, just due to the volume difference, but then will equalize. I'm not sure of that, but it kind of makes sense to me.