Currently in Collaborator (up to 13.1) there is only a single server-side global setting for restricting access to reviews (Admin > System > Access Restrictions > Restrict Access to Review).
We want to customize this on a per-group basis. Some of our groups want to allow Group Based by default, others want Participants and Group based to be the default, and still others want their group's reviews to be available to everyone.
Thanks,
SDK