Matthew
When running BC-HCE - as you create a Jobsite - in the top of that dialog you can select where you want to send the Sites / Designs for Earthworks machines - either send to your local PC or to TCC.
If you select TCC then it creates a Filespace on TCC called Project Library. Then when you Publish to Library in BC-HCE it sends all the Sites, Designs for Earthworks to the Project Library on TCC. I just created a project called UK Test and then a Design called Design 1 and then published to TCC and this is what you get on TCC.

As a partial solution to what you are trying to achieve - you could treat this Project as a Master and have all the Designs set up there on TCC. If your machines Sync then they will get All Projects and they will also get all the designs for all the projects. So no matter what you do here, you really cannot stop all your machines getting all the data - the best you could do would be to copy the folder system for the Project down and rename the Project as suggested yesterday to eg Machine 1 - UK Test, Machine 2 - UK Test etc. and then copy all of the project level data files to all machines, but only copy the designs that you want to the specific machine "Project".
That way - while all machines will get all the projects and all the designs, if they in Earthworks select the Correct Project (for their specific machine) then they will only get the designs in that project that you want them to have.
I just copied the Site Folder system as shown below

So now when a Machine syncs, they will get two projects - but if they know they are Machine 1 then they could load that Project and then they would only have the designs that you give that particular project by Copy and Paste in TCC.
While this will work for a few machines and a couple of projects - it likely will not scale to many projects and many machines. The team is well aware of the issue (based on (discussions this week) and there is work ongoing to make this better and faster for you as a manager.
I guess watch this space Matt
Hope this helps a bit at least in the interim period.
Alan