I haven't done the D9P, but imagine lots of seams intersecting. I learned never, ever to press open on quilts;that's for clothing. BUT, reading this Board, it seems many do press open adn don't have trouble. Recently my LQS offered a class that had us making a bazillion (not really, but seemed like it) pinwheels. All stitched to one another. Mega seam time, so I did press the seams open between the rows to help it lay flat. Rules were made to be broken, right?