I, too, have dried my prints on window screens and still got some curl on the fiber prints. What I noticed is that the print side gets completely dry but the back may be very slightly damp. I don't know if this is sacrilegious, but I take them at that very-very-slightly-damp stage and sandwich them between two pieces of scrap archival mat board, weight them down and let them finish drying. They seem to dry perfectly fine with no damage to the image...and they're really flat. Your thought?