The whole psyker scale thing is enormously vague and inconsistent.  If you were going to break it down realistically, it'd be "blank," "normal human," with varying degrees of "well sometimes grandma got premonitions about when the kettle was going to boil," then "psyker," "special character psyker (such as Gorsy and Lydia,)" and finally "plot armored super duper GMPC that can do anything," which is where the Alpha-Alpha Plus types hang out.