We know these use ESPN’s recruiting rankings, but these are hit-or-miss at best, and truly non-predictive at worst. That is not to mention that they have (in my opinion) the worst recruiting rankings of ESPN, Rivals, and 247. We know that there is some sort of recursive formula in it which considers (at least) Strength of Schedule.
https://www.reddit.com/r/CFB/comments/3u86sf/can_anyone_explain_espn_fpi/