Prefixes like obo in obo:NCIT_C16612 are not defined in Beacon context, so it might be better to not use them at all. Unless I am missing something and JSON-LD style IRI expansion can be used here? (like so https://www.w3.org/TR/json-ld11/#example-39-iri-expansion-within-a-context)
If not, perhaps replace obo:NCIT_C16612 with either NCIT_C16612 or preferably the full IRI: http://purl.obolibrary.org/obo/NCIT_C16612.