Why does our 5'6" receiver not do more comeback routes?

You would think that less than 10 years after having Darren Sproles on our team that CSP would know how to use someone with Harris' size and speed properly in the passing game.
Well, Darren Sproles was a receiver coming out of the backfield. A lot of the concept created for Sproles was used for Kamara.

Darren Sproles as a LOS WR wasn't that productive. Harris is exclusive used at the Los scrimmage.

Even though, Harris is the same height. He is more comparable to Steve Smith and Tyreek Hill. Who also got 3-4 more inches on him.