Steve - just a thought - are you adjusting the focus (parallax) when you change between 35 and 55 yards? I had a scope where changing the parallax would change the POI. Actualy it was not the POI changing - it was the point where the crosshairs were lining up on the targe which changed.

The reason I ask this is because I find it difficult to get my head round the crossover theory. If you are zeroed at 30 and out by (say) an inch at 60 yards - then assuming light and pellet travel in straight lines (pellet when viewed from above ), then your scope would have to be 1 inch out from centerline. Or am I missing something?

ATB Gordon