Regarding my own opinionated thought on the CPP.
Here is my guess of what they are focused on two aspects.
Your actual performance in their tests. In the second round, this includes the Numeracy Tests and the JKI quiz. For most people, I think they pass the above two with out too many issues coz they aren't too hard to prepare for.
They also take a comprehensive look at your "Judugement/Decision" making abilities under a number a circumstances. In a group / In the interview / Under pressure in the flight planning exercise.
What I mean from "Judgement / Decision Making" is the whole process... From taking in the bits of information , processing it , the giving the response.
I would guess that 70% of candidates fail the second aspect of it.