Firstly, thanks for all of these fantastic images. Best I've ever seen. Do you have any more of the entire ceiling?
Anyway back to business.
How about the entire northernmost block complete with curved section is all carved out of one chunk of stone?
I say this because the next block up is rectangular and would therefore be about the same proportions. Most of the remainder seem to be squarish.
Also they are all of constant size in all the drawings that I've seen, which seems to be incorrect.
If we can get hold of images of the rest of the ceiling it may be possible to stitch them together, or at least make a more accurate drawing.
Looking at the M&R drawing, it seems that he's drawn the curved block (or curved section of a large block) with a flat at the northern end morphing into a curve. See diagram. Or at least a non linear curve. Your photo seems to back this up as there's a hard shadow fall off, bleeding into an expanse of constant tone. (flattish morphing into tight curve).
If it were a curve of constant radius, (a chord of a circle), we'd see a more gradated shadow fall off.
All of that probably makes no sense whatsoever.
If you need a better drawing let me know.