A quick question for Synapse 25 owners....is the back of the pack flat from top to bottom? The bottom of the back of the Synapse 19 curves away from the back of the wearer. This creates a problem for me when placing file folders in the 19 as they get curved rather than stay flat. It was the reason I couldn't keep my 19. I can't tell from the photos if the 25 is the same way.