Just out of curiosity, i revisited the overtone exercises in JF’s Altissimo course.
I managed to do all 7 overtones on all 4 Low keys. However I found two overtones a bit scratchy the 2nd (Bb) and the 5th (D) when using the Low Bb fingering. The 2nd overtone i had to lower the tip of my tongue, and the 5th i had to open my throat and control the air pressure.
In future i will incorporate playing overtones at least once a week, i found it strengthened my altissimo notes.
Seems like long tone exercises are good for playing good pitches,
and overtone exercises are good for playing altissimo pitches.
Another thing that surprised me when i revisited the altissimo exercises, i found i can make all the fingering positions work.
The last time i looked at the altissimo course many years ago, i just stuck with the fingering positions that i could get working, from G to E#, and never thought about going back to the course.