Tradition 9-patch each square is 4½" before sewing with ¼" seam leaving finished size of 4".
When you cut the center squares in half & resew with ¼" seam the strip has a finished size of 1¾"
With these dimensions the D9P block has a finished size of 11½".
12" is bigger than 11½" by 4%.
Instead of 4.5" you need to cut 4.674 (Sorry about switching between fractions & decimal)
4% of 4" is .174 which is approx 11/64 (greater than 1/8 but small than 3/16)
.174 plus .5 (½) seam allowance = .674 or 43/64".
Improvise. A whole lot easier than attempting to be this exact with quilting tools.