I guess you're right, but what struck me was the difficulties you're having with distances between the sites and the curvature of the earth etc. These guys are saying they've witnessed solistical alignments all along the Boyne valley, from Drogheda, to Slane, to Loughcrew (not in the Boyne valley) that seem plausible. I know you're dealing with greater distances, but Loughcrew is roughly about 50kms from Drogheda, with Slane in between, so maybe you need to work out what's of significance between the sites. Or maybe you have already. Or maybe you don't and I'm just raving! :-)