Put a slightly larger dia front bead on the gun and it'll pattern lower for you. Nothing changes actually but you will put the bbl(s) lower on the target/bird when you sight along the rib.
I know many say not to look at the front bead and that's most likely true. But for most of us we need the bead to guide our eye(s) to the muzzle and the target.
I'd be willing to bet you used the front sight bead to draw a fine 'bead' on that orange dot on the patterning paper. A larger dia bead will drop the bbls a bit as you take the same sight picture over that bead. It doesn't take much.
Also might try shooting some paper patterns by just throwing the gun up to the shoulder and firing as you would at a clay target. No 'aiming', just a field shooting type shouldering and cheeking of the gun and shoot. You'll see where the gun shoots for you..it won't necessarily be where the patterns are in the pics.

Different shells/loads will pattern wildly different at times also as will just changing shot size. A low recoil load may pattern lower as well.
Nice even patterns!