This from the FAQ could really do with a brush up!!
When you win a game in Arena mode, you gain Arena points. You gain 3 Arena points when beating an opponent from the same league, 2 points when beating an opponent from league N-1, 1 point for beating an opponent from league N-2, and so on (and the same for higher leagues).
When you lose a game, you lose Arena points. However, you cannot go below 0 points.
It implies for winning at N-3 there would be 0 points, N-4 would be -1 point
I think what's happening is this:
Win league N+5 = +8 (Bronze player beats Elite player in a six league model)
Win league N+4 = +7
Win league N+3 = +6
Win league N+2 = +5
Win league N+1 = +4
Win league N = +3
Win league N-1 = +2
Win league N-2 = +1
Win league N-3 = +1 (because I can't believe you'd actually get 0 points in the progression!)
Win league N-4 = +1
Win league N-5 - doesn't exist as Elite players not ranked on arena points
The flip for losing would be:
Lose league N+5 = -1 (Bronze player loses to Elite player in a six league model)
Lose league N+4 = -1
Lose league N+3 = -1
Lose league N+2 = -1
Lose league N+1 = -2
Lose league N = -3
Lose league N-1 = -4
Lose league N-2 = -5
Lose league N-3 = -6
Lose league N-4 = -7
Lose league N-5 - doesn't exist as Elite players not ranked on arena points
Apologies if this has been done before. I'm trying to get my head around the merits of playing wide variations in leagues. For players in higher leagues there may be limited upside benefit playing down too many leagues, and considerable downside in a loss.