Good question - and it all has to do with the offense's alignment. Against 21 personnel (2 back, 1 TE) with the TE attached, the SAM will line up on the line like a stand-up DE. Against 3 WR sets, though, the SAM walks out over the slot (as Werner and Darron Lee did quite often in the past). Mattison plays a lot of nickel against that kind of personnel, so it's possible that the slot defender becomes a DB more often than not in today's game.
Unlike when Wade was put in as the Nickel corner this past season, that DB won't just be playing the slot WR in man-coverage. Rather, they'll often be an underneath zone defender asked to play the run on many occasions, usually filling as the contain player. So, the question becomes who on the roster has the skill set to play that role? Does White or Fuller drop down in the box with Pryor or Riep filling in as a deep safety? Vice versa? Does one of the corners slide into that role?