@AndyD thanks! I'll try to see where I'm sitting, and if I can lean more to the right. That's very helpful!!
@bernard omg! doing the mirror thing is brilliant!! I'm also going to try to do the LH rolled chords an octave (or two!) lower and just see how it feels, because I haven't tried that at all yet.
These two things (mirroring and moving lower on the keyboard) might also help me decide whether to use the thumb on the top two notes.
My current teacher has very small hands, like, to my eye, dramatically small. I'm 5'4" and have probably a slightly larger than average reach for a woman. She is quite petite, maybe only 5' tall, and her hands are very small and her fingers look short to me. But of course, she can get her hands to do all kinds of things that I can't. So I think the thumb on two keys things is probably something she has to do. And it sounds fab when she does it.
But I'm not sure I "have" to do it this way.
So I will try all these ideas -- leaning to the right more, mirroring to see how I'm using my body when the roll is in the RH, and then also playing lower on the keyboard to see what fingering feels natural -- and then go from there.
To your (@bernard point about making up exercises -- I was trying to play just the top three, 3-2-1 and it's really getting over "c" that is the problem. (also I think my 3-2-1 spread is stiff)