Be sure to have the brake mechanic tapes the rotors before turning them!:D
And listen folks: if you are going to geek out with calculations, etc. be prepared for someone else to out-geek you with even more equations, etc. They are just trying to get things RIGHT, and you are the one who opened that can of worms.
A single piece of tape doesn't do a whole lot. When I did my double bevel, I was trying to emulate a Feather edge (as per the Zowada website ~22 degree angle), this required me to add 5 layers of tape to my spine prior to honing.
Didn't do squat for shave performance. Overall just a pain in the rear, especially to un-do that bevel.:rant:
Tape to protect the spine seems worthwhile if you care to do it. To tape for the sake of improving edge performance, I have some definite reservations about!
But, you don't know until you try!