Brendan
WKR
My reaction is that you don't have a spine issue, it's a tuning issue and maintaining consistent form.
When I shoot bare shafts and make adjustments - I want to make sure I'm getting the same result every group. If you get a bare shaft low one group, then in the group or high the next group, it's you and not the bow. Better to stop shooting, rest, and come back later. Sometimes I get too tired to shoot reliably and push to another day.
Your first adjustment above did what I'd expect - got you closer. Your second adjustment something strange was happening, maybe your form?
I'd go back to that first adjustment (nock level) and shoot some more groups with bare shafts, and test field point vs. broadhead to see where you're grouping. Look for consistent results before making any changes.
When I shoot bare shafts and make adjustments - I want to make sure I'm getting the same result every group. If you get a bare shaft low one group, then in the group or high the next group, it's you and not the bow. Better to stop shooting, rest, and come back later. Sometimes I get too tired to shoot reliably and push to another day.
Your first adjustment above did what I'd expect - got you closer. Your second adjustment something strange was happening, maybe your form?
I'd go back to that first adjustment (nock level) and shoot some more groups with bare shafts, and test field point vs. broadhead to see where you're grouping. Look for consistent results before making any changes.