Very nice shooting there Dave. I'm not sure why the sights do that after an adjustment. I've had a couple rifles do that to me also.
Maybe you could possibly be canting the rifle slightly. Try cranking down the sight and see if it shoots low left. Or move it down where it was and set the front sight a little higher in the rear sight "U". If you're canting the rifle a bit both methods should move the POI horizontally.
That little bit of movement would only take a couple degrees of cant.

I believe you'll find out it's actually the stock weld. If a person doesn't mount the rifle the same way it will cause a slight change in impact due to the positioning of the eye and how the sights are viewed. Case in point shoot an AR platform rifle with standard peep sights. The shooter needs an anchor point to accurate shoot. I always taught touching your nose on the charging handle. That way there is a constant anchor point that places your eye in the same location so the same perspective of the sights are viewed. Just my .02 cents. Still good shooting cayugad.