iMHO, the working section of the chart should start about 25" up from the floor. Since the panels run selvage to selvage, that would be about 40". Then add whatever border width (if any) you like.
Example: if you plan on 2" finished borders, the bottom of the finished quilt would be 23" (or so) above the floor, it would be 44" long in total, and last until your DGG is 5"6'.