I was hoping the skull measurements usage would fall along the same lines, that being measurements specific to both the castaway and Earhart. Reading up on her skull caps ( flying helmets)...I suppose the soft leather would allow for a fit onto any number of heads, if the dome were large enough to allow, so maybe using a standard hat would be more preferable, should one decide to conduct such an experiment to whittle away at the 1% doubt.
The one thing I reason is, if the Niku skull measures too large, to fit into one of Earhart's hats, it could pose a problem,....too loose, maybe not so much, as many photos I see of her, her hat is almost ear touching, too well below top of ear.