Been a while since I did spiral cut ham. I think the edges dry out slightly.
I did a quick Google search. Get a bone in spiral cut ham (is there boneless?). Cover ham with foil or a lid, I’m thinking why not do both? Flat side down, not sure why you’d cook it on its side. Since it is pre cooked, do not over heat.
While technically there is more surface area, the slices are sealed laying on top of one another. But if you overheat, that’s when the meat starts shrinking and edges start curling drying the edges out first.