Ed Doe, first of all thanks for the research, what you have copied is spot on, however it is a generalisation and the actual problem is more complex than written, it's dumbed down for the internet. The problem with generalisation is that by its very nature it is unspecific, brake bias is fundamentally calculated from the centre of mass of the vehicle, as we all know this changes with acceleration, so for road use designers will stick to a pretty large margin of safety given the infinite variability of the road and car, for racing cars it becomes track specific (in F1 they even change brake bias through the lap).
I have no idea of the % bias of Jonny's zed, I would bargain no one here does, but I guarentee the manufacturers of these brake products will have done their math and will recommend something suitable, at the end of the day Jonny asked and they told, they ARE culpable