Size of d1 often plays a huge role in terms of final/D1 ratio, even in excess of genre/demo/sequel considerations -- those things are important too of course, but they play into size of d1 itself so they don't have *that* powerful an affect once you condition on that. Reception can, but it’s unknown in advance.
Thor start basically is too big. BP2 is probably single best comp if I had to pick one at gunpoint, especially now that AM&tw2 start looks like it may be 70% if bp2 rather than say 40%, but if you're coming to one movie which it's doing ~70% of it's often useful to have another which it's doing like 1/.7=140% of to balance out, as long as it's pattern from d1 wasn't too dissimilar from reasonable genre/franchise dynamics. In this case that is avatar 2, which had a very CBM typical final th/D1 Th for it's D1 Th size despite legging much better after.