Oh....I see. Sorry I mis-understood your question. There are several ways to approach pressing the seams on the back.
Since you are using flannel, you will probably want to press your seam allowances for each seam to one side. Try to press alternating rows in opposite directions so that the seams will "nest" together, or "kiss" and make a neat intersection for the next seam. You will find lots of GREAT info about piecing in Alex's TQS classroom here:
[url]learn/classrooms/[/url]
There is also a method that I call "twirling" where the seam allowances are all pressed clock-wise or counter-clock-wise, so that each intersections is really flat. It takes some effort to figure out which way to press all the seams to get them all to spin, but it really does distribute the bulk nicely.
Here is a photo of how I twirled the intersections of my 2010 pieced BOM:
Hope that is better info for you!