I find that fine tuning the mandolin in the white the hardest part of the entire process. Simply put, I don't have enough experience doing it.
What things do you listen for or feel for when trying to bring out the best of the tone? Is there a particular string+fret that you play that helps steer you in the proper direction?
As an example, I find that the G string at the 5th or 6th fret sounds too cold and hard when my back plate is too stiff. Consequently I find that the 4th string at the 4th to 7th frets sound too hard when the top needs sanding.