Eureka! My theory was correct. The small podium at the base of the obelisk is definitely responding to the artifact's proximity and vice versa. Honestly I feel foolish for not attempting this sooner! The stylistic similarities between the artifacts and the obelisks floating above the island seems so obvious to me now. Clearly they were created within the same culture and era.
Bizarrely, while both the artifact and obelisks are in exquisite condition, there are no other signs of this mysterious civilization. How could that be? What kind of mad society would galavant about some remote island, building towering structures and stuffing knickknacks into caves before vanishing without a trace? I don't understand it, but it's certainly piqued my curiosity.