As you stated there are a number of positions on the fretboard where you can get natural harmonics. I'm sure that everyone will agree the most natural harmonic is at the 12th fret. You can get harmonics at any fret anywhere on the fretboard if you do it right-for instance if you want to get harmonics for a B note, depress your left hand finger (if you're a rh player) on the 2nd fret on the "A" string then lay your index finger of your right hand lightly on the 14th fret of the same string and strike it with your right hand thumb (towards the pickup side of the 14th fret) you are simply moving that 12th fret harmonic around the fingerboard as you need it.