Organic Groups (OG) Setup:
3 OG group types: departments, committees, and restricted_groups
Department groups: Department A, Department B, Department C

What I want: A view of users with an exposed filter of "department" OG groups that they could belong to.

What I have: A view of users with an exposed filter of *all possible* OG groups ("department", "committee" and "restricted_group") that they could belong to.

I cannot figure out how to limit the filter's list to only the OG group type of "department". Under the filter's options, I have the following settings:

Expose this filter to visitors, to allow them to change it = checked
Filter type to expose = Single filter
Required = unchecked
Operator = Is one of
Options:
- Select all = unchecked
- Array = unchecked
- Array = unchecked
- Array = unchecked
Allow multiple selections = unchecked
Remember the last selection = checked
Limit list to selected items = unchecked

I don't see an option to limit what groups are displayed, so the filter displays a list of all OG groups. I've tried all kinds of combinations of contextual filters and regular filters, and checked and unchecked arrays, but I just cannot figure this last step out. It seems like it should be something simple, but I'm stumped. If you can help me to figure out what I'm missing, I'd appreciate your help.