I must admit I'm amazed that people fly like this - I never could, and still can't!
I just adjust the thrust in the way I would alter power if flying a smaller aircraft, and it works - for me, at least.
On a more serious note, if you are going to do this mathematical stuff, you'll need to consider wind... Do any of you factor that in at the 'What N1 do I set to start with?'' stage?