After some experimentation, heres what I found
If I set the Limited group the following access at the parent folder PROJ
Traverse Folder/ Execute File
List Folder / Read Data
Read Attributes
Read Extended Attributes
Read Permissions
And make sure the scope only applies to the Folder Only
Then the users can see PROJ, can't see any files in it, nor the sub-folder Data, but can see the sub-folder Docs. And with Full Access set on Docs means they can see, read and edit files in that sub-folder.
However, if the nesting was deeper
PROJ\WORK\FILES\Docs
I'd have to set the above permissions to each subsequent sub-folder, scoped to Folder Only, prior to Docs to be able to gain access to the Docs folder and files.
I'm sure there has to be a better way to confer this.