A little small, ain't it?
Looks pretty good, though. What Phil said!
Honestly, when looking at it, I wasn't thinking about vortices forming, but he's right. Also, if the side-flow angle is too steep, it will hit the flat spot of the corner of the bed, and create a higher pressure zone there at the tail, which could disrupt high-speed flow. You'll see what I mean if you do the mini-air-chamber test. Water would show it more readily. You'll see that one of your streamlines will follow the shape and create a bubble effect at the rear corners of the bed, and if you then lift the streamer slightly, you'll see that it separates from the shape of the cover at some point about half way back, as it should be dipping over the side.
I'm not 100% sure that this will happen, but it's the biggest potential downfall I see to the shape, once it's on a vehicle.