Yep, the higher the note, the less air used.
I really feel the value here is remaining PASSIVE. I think an E would be the best note. Any higher can encourage unnecessary, negative tension.
My big issue with the Whisper G Cat Anderson method, whilst it has plenty of merit, it encourages activity that people don’t recognise. When done on a low C, you are less likely to engage involuntary or unnecessary muscles.
Interesting topic!!!
Cheers.