Robert,
I don't see subgroup in the menus of GMF or your test group (I don't yet
have my own group).
You don't because in both groups the option is set to "Owners Only" - I think that's the default.
In my test group you're a moderator with the privilege to change group settings, so if you'd like to play with subgroups feel free to change the option to "Moderators and Owners" or "Subscribers".
-- Shal
Shal Farley