When doing my D9P after making the block, I measured the center section/blocks and cut down the middle. You then turn the board if you can and cut down the middle of the others to form a four patch out of your oringinal 9P block. If your finished center blocks ended up exactly 4 inches sewn, then cutting at 2 inches would be correct. Since very little I sew comes out exact, I just center my cuts. A clear as mud answer right?