Currently per share masks are configured globally, as per the 20shares file:
-o "create mask = ${OMV_SAMBA_SHARE_CREATEMASK}" -n \
-o "force create mode = ${OMV_SAMBA_SHARE_FORCECREATEMODE}" -n \
-o "directory mask = ${OMV_SAMBA_SHARE_DIRECTORYMASK}" -n \
-o "force directory mode = ${OMV_SAMBA_SHARE_FORCEDIRECTORYMODE}" -n \
Currently adding the same directives in "extra options" will override these, but only because they might possibly come after the above.
It might prove useful to specifically expose these four masks in the web UI, and use the global defaults only if they're not provided?