They are merged onto the built-in defaults, the way the proxy's additional_policies and OC_ADD_RUN_SERVICES are, so the name says it: env variable, yaml key and field all carry the prefix. The two that take key:value entries are named in the plural like the other map-shaped settings in this repo, and the README says which of the three takes bare mime types.
Dominik Schmidt
8e508e56c2