You are not missing the point. And congratulations on your great discipline in running tests and keeping notes, something I myself have never managed to profit from.
My own method is similar. Tx400 @320, 10m @ 75f is "standard." If the light was generally harsh or contrasty, then stand develop for the last few minutes. If the light was "flat," then let stand for a few minutes past standard development. Not very scientific, but it gets me close.
Sounds like you have a pretty good idea. Thanks for reminding me to go find that McLean book.