Yes, it’s Appendix F goes over it, if you look him up you’ll see that’s one of his areas of academic study.
No, I did my own version though may try the original, I can’t remember if I used it (probably, but it didn’t stay on my list0, I have theories on creating original work, if you want to see my totally anglicised version it’s here: My Invocation Of Inner Divinity.
Did it feel like the physical strain on your larynx, or an energy blockage?
I use the Stoicheia exercise from the book (cheatsheet in the link above), kind of daily for long stretches then I do something else, always come back to that though. 