If Planet X had a perihelion around 60 AU and an aphelion in the vicinity of Sedna's aphelion (940 AU), would it be considered to be responsible for both the high eccentricities of TNO's orbits and the Kuiper cliff, the abrupt outer end of the Kuiper belt at ~50 AU? Or isn't it expected that the planet would have a that close perihelion? If so, why not? Except Eris and Sedna, there's no other (dwarf) planet that would be at their current distances, after all. We would have already discovered it, right?