Anatomy of Another Phrase

I was going to just call this post "Anatomy of a Phrase" but that phrase (LOL!) sounded familiar. That's what I called this post and it was about the same kind of phrase, an ascending phrase that sits on a high note that's problemmatic.

So OK. For me the distance between an A and a B flat has always been like crossing the Rubicon, but I've now noticed something else - the distance between an A flat and an A is like crossing the Rubicon if we're talking about singing pianissimo.

I can always sing an A if I can sing as loud as my body needs to to keep my larynx down, and I can always sing an A flat pianissimo by opening the back of my throat as if I had a big wad of cotton back there.

Just for the record, I have never had a whistle register, a flute register, or even a real falsetto above a G (I can sing certain legit musical theater pieces and some choir soprano parts in what I call my "fake Julie Andrews soprano" voice, but again, that doesn't go above a G.)

What I'm struggling with now is the Introit to the Mozart Requiem. I'm on the soprano part (as a high-ish - at least high by choir standards - mezzo I switch parts a lot if I'm not on my home base of second soprano) which is fine, in terms of tessitura, until we get to a phrase that goes up to an A and sits there for a minute or three (I may be OK if we sing the piece a little faster than it is on the recording, but I should be able to sing it with the recording.) Now let me be clear. If I can just drop my larynx and sing I don't have problems. And in the past, that would have been how I would have approached the phrase until the choir director told me to tone it down. But now that there's a real coloratura soprano in the choir (and a musical theater ingenue, who can sing up there, as well), I am suddenly much more inhibited about singing a note like that, which is the last thing I need.

So far, not much has worked. The little "fishmouth" that enabled me to sing a soft high A in Randall Thompson's "The Last Words of David" on the word "Allelooooooooooia" isn't working. Cottonmouth isn't working. I just can't do it that extra half step higher. Humming is a crap shoot. Can some people hum higher than they can sing? I can't. The highest note I can hum reliably is a G. I can hum a lot lower than I can sing. ...I can hum down to a low D whereas the lowest note I can sing anything that you can hear is probably the A below middle C.

Yesterday, when I was feeling so depressed (about my ongoing eldercare situation) and had a bad allergy attack, and was going to scrap the idea of practicing, I sang some arpeggios (up to a C!) and then set to work on what I call for short "measures 40 and 41". Dropping my larynx and singing it on "oo" (someone else can sing the words) I got a sound out that was maybe only 70% as loud as my "natural" sound up there, but I

don't know if it will be quiet enough
don't know if I can do it off the cuff sitting in choir practice

Well, the good news is I'm having a lesson today so I can try to come up with a "plan of attack", no pun intended.

ETA: I had a lesson yesterday and we worked that phrase to death and came up with something that, in the mirror, looked like the "little fishmouth", but didn't feel like it. He told me to think I was pulling taffy. He also said it didn't help to skip "Requiem" on the Fs. I should go from the F to the E, take a breath, start a bit late on a mezzo-piano with my mouth small, and then imagine I was pulling taffy and decrescendoing. I must have sung that phrase about ten times. Well, if nothing else I have it memorized. Now. Will I be able to do it tonight sitting down in a group of people? When I was the only "trained" singer in the section (except for the other mezzo struggling with those notes) I felt more "entitled" to do "silly" things like stand and look in the mirror (how I got through "The Last Words"). Now I feel embarrassed. If all this is so easy for the two young sopranos, why is it so hard for me? None of which helps me. I need to stay in my own zone and try to block other people out, like a tennis player on the court working on a difficult move.