But at least from a different perspective...

I have a carb and Si mid-80's Preludes. I was messing with my Si brakes have no 'bite' after completely replaced brakes. The original rear rotors I took off were rusty after an 1800 mile drive home and in bleeding the new parts I never got any 'squirt' from the bleeder
It turns out the carb has a 3540 while the Si has a 3030... which I'm assuming is a significant difference after reading about the range of them that come on Civic/Tegs.
Doing more comparing, I came up with this...

I find it strange that a nearly identical car has seemingly such a significant difference with only 100lbs more and 1/8" bigger front caliper (they are also the same size 9.5" rotor). I like one theory I saw that the numbers are Front and Rear pressure distribution (since they are called "dual" proportioning valves) ie. 35% to the rear, 40% to the front. Because I believe that these are meant to control lock up correct? So to move the proper volume the master bore sizes are matched to [primarily] the front caliper piston size, which is in turn chosen for expected weight and heat distribution.
I'm not sure how all that fits into my numbers there, but.. this was just a lot of thinking out load apparently....

 

The numbers cannot mean a proportion of 100 percent rear/front because both 4040 and 3030 valves exist.

The Honda proportion valve has a break pressure where it will release the rear brake pressure under lockup and that is likely what those numbers signify. .