Hi John,
I’ve had good success using the F-sharp and G double octave harmonics in the Presto Status Stage, but I continue up chromatically to High C, incorporated into my daily warm-up. It’s great for working different dynamics and achieving the balance you refer to. In working above high C I try keeping a mental picture of the bar straw between the lips. The clearer the mental image the clearer the sound for me.
Have a good day,
Brian