So there's been many threads about it back and forth as to why the amounts vary based off of wins. We all know that it's the same for losses, but after actually getting people to talk to me about their rank and workshopping it through this grind, it's very apparent that it has nothing to do with the rank Your opponent is. It is solely related to the rank you are.
The lower the rank you are, the more RP you get for a win. Simple as that .. it's diminishing returns by rank threshold.