I didn't have any trouble when I had a 6620. Some guys around here take the 2 outside fins and reverse them so they spread more to the middle and some have done that and then "straightened" them out a bit.
look at the wear pattern of the cylinder bars. It sounds like maybe the crop is feeding down both sides of the combine and not in the middle. I would think that a 6620 would be narrow enough that this would not be the case, but I have seen it happen in 8820's. The only cause I can think of would be that the header auger flighting has been trimed back for a wider combine.