I've always wondered (not being a truck owner) why if job boxes at the front of the bed butterfly open, why not an entire aerocap?
Of course, were I to have a truck the reach-over height wouldn't be much more than the tire height. My son has a Silverado, I can barely see over the bed.
A good starting point would be a spoiler/half tonneau like this
Maybe chamfered on the ends for tumblehome.