The standard in data is to
I like your thought but have always looked at it a bit differently. While you want to look at the max pressure of the system, many times that is not what is available to use in a corner. Say the brake zone is slightly downhill, like Turn 7 (The Chute) at Watkins Glen, you have less braking efficiency and capacity than if the track rises and compresses the car like Oak Tree at VIR or Namerow at Mont Tremblant. The maximum braking effort really changes lap to lap, corner to corner, but we can make some good generalizations like a car can brake at X g force, or X brake pressure. That works great on the bar graphs for the video. If you want to get down to the fine details, you really want to jump into the data and see the actual numbers. If you want a really deep (and neat!) dive, check out the video I did with AiM on "Cornering by the Numbers"
For the actual bar graph, it's showing percent of total effort the same as if you were doing a math channel. Either way you are picking a maximum. IMHO, doing the math channels is much more involved than just putting the max in the bar graph location. For someone who doesn't have a brake pressure sensor, you can use a bar graph with Long G as a great proxy for brake pressure, setting the max to something like 1.2 Gs (a guess for an SR).
As an aside, I'm surprised that the pressures are only in the 8-20 bar range. In regular cars and most sport racers, we run 2,000 psi, 100 bar, or 160 bar sensors.