Use a light color fabric, tone on tone print would be OK, for the center square. Remember to prewash the fabric and NO additives like softener or starch or such. Just iron the fabric to freezer paper cut a bit larger in length than needed, then trim the excess away and repress. This is your 'leading edge' to go into your printer.
I do NOT use best with my printer as it is too much ink. After printing I re-iron the fabric to set the ink.
With signature pieces I make a frame, usually from a file folder so that those signing can only sign within the area I cut out. I first tried just marking the seam line and explaining where to sign but found that didn't work. When I used a fram all the signatures fit like they were supposed to.
I think I put a written tute on the QB about this.
Have fun with it.
ali