870 POA/POI way off.

[Ridgerunner7]

Right on at 20, hitting 4-5" high at 30, and hitting 8-9" high at 40 yards.  This is odd to me because my 12 ga pattern drops at further distances.  Why is my 20 pattern rising?

My 12ga 870SM shoots dead on at 20, 3-4" low at 30, and 7-8" low at 40 using the Heavi Shot 13 #6s.

What up with that?