Spagnoulo (and his predecessor Jim Johnson, too) has always been an interchangeable safety kind of schemer. From Brian Dawkins to Quintin Mikell to Gibril Wilson, there have been players with a "FS" designation that get put into positions to make plays, particularly in subpackages. Offenses no longer routinely put their TE (or the 2 WR side) to the quarterback's right, so the right safety (in the interchangeable scheme) gets plenty of strong side duty. If that player has the talent, he'll be used as a rover, a hybrid nickel backer, a force player in the box and other roles that put him around the ball. Mikell may not be a 90 solo player in this role, but the guys who have played this role before (including Mikell himself) have been very productive statistically. In the end, as we're seeing more and more often, the depth chart position should be a starting point for your research and expectation but it's frequently dangerous to fall back on the time-honored defaults when matching the depth chart position and potential IDP value.