I wondered about disappearing 9 patch myself!

I think you may be making it harder for yourself (we all tend to do that at times). You are simply adding a strip to a charm (5" square to a 2.5" x 5" strip). Then you are adding a 2.5" square (cornerstone) to a 5" x 2.5" strip and adding that the other piece. Take a look at just one block in the quilt and it will be easier to see.

We are doing the D9P, I printed the photo as a possible layout.

The finished proportions will be different if using same-size strips/blocks for making it D9P method.

See attached.

After measuring the picture, it seems like the proportions used are approximately 3 to 7 (by using 1/8 inch increments on my screen) or 6 to 13 (by using 1/16 inch increments on my screen.

One can adapt the d9p method to making any of the units shown in the attached drawing.

One just has to figure out what size to cut the strips to make it work.

If you want to strip piece a "modified D9P" that will make a 9" finished ABCD unit, this might work:

The third drawing with the cutting lines should have matched the larger drawing - but I did not want to redraw it. I hope you can imagine that they are the same.

If you do the disappearing 9 patch using 5" charms, after you cut the block in to 4, the resulting blocks will be 7", exactly the same as the original block mentioned. If you cut a charm in half you will have (2) 2.5 x 5 for the sides. If you cut a charm into 4, you will have 2.5 x 2.5 for the cornerstone.

jafter allowing for 1/4 inch seams, the "finished" size of the ABCD unit will be 6-1/2 inches. the "unfinished" size of the ABCD unit will be 7 inches.

the original poster sent a pm to me that she wanted to make 9 inch ABCD units, that is what the last drawings were for.