Not being able to pick up short yardage downs has been a lingering circumstance going all the way back to when the Dolphins last had a fullback. Lousaka Polite had an astonishing ratio for gaining that short yardage first down throughout his tenure on the team. Also there are the trending changes that the league has made moving away from integrating the fullback position.
As good as Lamar Miller was one of the hooks on him was that he suffered in this situation. Also whether he could hold up under a more bell cow like workload. We may see this part play out with him in his new role in Houston.