I'm slightly confused on what you are seeing, but the classic case when close to the right load is for a tad more powder to move things in the cross eyed direction and a tad less to move things in the wall eyed direction, ther change in barrel dwell time having a greater effect than the change in impulse due to slightly more or less powder.

This is why some doubles will regulate with a very light load, the impulse is way down but the dwell time is way up and there's a second sweet spot.

But when it's all said and done the rifle will do as it damn well pleases. This due to the barrel vibrational patterns which are not predictable.