I had always assumed that whatever the "percentage" is, it works like this (for simplicity sake, I am using 1 for a D prestige and 0.7 for the "percentage").
D = 1.0
C = 1.7
B = 2.4
A = 3.1
In the sample from before, let's say CV's are worth 100 points for a D prestige school, here is how I think it works:
School A = 10 * 310 = 3100 points
School B = 16 * 240 = 3840
School C = 25 * 170 = 4250
School C wins, server does not go down. I could be wrong, I guess, but it seems like the most straightforward way to implement this. Maybe the issue is terminology because it is not a true percentage difference between the grades.