I think Kupp, Jefferson and Atwell can all lineup at any of the WR positions and I expect that trio to be on the field bunch, especially the first 2 guys.
Let's face it Atwell is really the only guy with the speed to really stretch the field. Jefferson and Kupp can get open deep but Atwell has the speed that can force the defenses to play deeper. If he isn't on the field we lose that aspect of the offense as nobody else has the wheels needed to really stretch the defense. Still Atwell has to show he is up to the task. At least at the end of last year he did show progress and has been a top performer in OTA's so the trend is positive.
