Julienm1 & Synnove the measurements that you have would be for a regular nine patch, however Elaine is asking for a
disappearing nine patch block to finish at 6 inches. If start with 2 1/2" blocks when it was cut in quarters and sewn back together, it would be at least 1/2" too small. Unfortunately, the math on the page
http://raevenfea.com/quilting/disappearing-nine-patch/ doesn't have the size to finish at 6 inches, because it is said "
some common block sizes, like 6″, 8″, and 12″, end up requiring the starting squares be cut to third-inches, so I didn’t include them above."