Well, yes, the tarp is on backwards but I wasn't going to front you out!
The narrow flap across the front near the top clips to the flap on the back of the cab cover to keep rain/snow from getting in between them (at least from above).
I always thought the cargo cover was a bit of a weak point as regards weather protection, with that open window at the front and the older tarps like mine having no rear flap. I use a rear flap from M-series trucks that I narrowed a bit to fit, works okay. The later tarps like yours with the rear flap look very weather proof except for that window. But you can always hang a small tarp inside like I have in the past to keep rain out.
Cheers