In RAS v.16.5 and below you can manage Inherit Default Settings for each Site only. But since RAS v.17 we have added the same settings for RDSH Group.
If a server isn't added to RDSH Group it has only Site Default settings. As per the screenshot below.
If the server is added to a group it has intermediate settings- RDSH Group Defaults.
If inheritance is enabled, Site Default overwrites Group Default and Individual settings. If Site Default is disabled, Group Default will overwrite Individual settings. But in both cases Site Default is master.
NOTE: Terminal server or servers must be added in RDSH Group if you want to manage them with Group Default settings.