After the physics’ theory, just was the experience (around many riders) who determined which is the most recommendable position or regulation for the different gearings, and finally we just drew a triangle for the most preferred regulation. Even depending on the sport the best regulation can be a little different, and so, the triangle for MTB is a just a bit higher than the one for road Rotors.
After that, the Rotors in the market confirm that most people prefer to use the recommended regulation more than one mark higher or lower, and I say that not because people use the recommended and be happy, but because I know many pro-riders and cyclists who have tested different possibilities and finally use the most recommended.