Bob don't get it totaly. I think i know what you want to say but i just don't get it 100%. If you'd care to explain some more or if you have some literature on that to read up. I googled it at first but didn't find anything usefull.
So for example at 50% pedal travel (not really travel but instead pedal pressure in a real car, of course), the brake balance could be 60/40, while when braking harder/fully it shifts more forward to say 70/30?
Aaaah. That's quite useful. The XRR could use something like that (the back just comes around and says hi at hard braking in 2nd or 3rd if you're not carefull).
This is what I think of when you say "knee point". It's a reverse-biased zener diode. (see attachment)
I think what is meant by "knee point" in the case of brakes though, is merely a point at which the braking response becomes non-linear.
For example, the first 80% of the brake response can be described by the function f(x)= x, while the last 20% can be described by the function f(x)= (1/2)x.
I was under the impression is was so that the rear brakes got more use under light braking (as is typical in road cars), thus increasing deceleration for any given pedal pressure. Since the harder you brake, the more traction the front tyres get, and the rears get less (absolutely speaking of course), it does make sense.
In a racinc application, this could let you have brakes that encourage trail braking more (less understeer) without compromising hard straight line braking.