Help with proper Sync setup

Anyone have this figured out yet?

I'm trying to set up sync properly and effectively.

Simple context:
1 NAS
2 Computers

- I have created on the NAS a folder called 'MyBox'
- I want the 2 computers to have the 'My Documents' folders synced
- I create a New Sync and here is where my uncertainty starts:
Do I select the NAS folder 'Mybox/My Documents' as the sync folder and then select
Local folder 'My Documents'? I don't want to sync to the Acronis cloud because I don't want to pay for the extra space and that is one of the reasons I have the NAS.

Then on the second computer a new sync shows up that I can join. I join and the select 'Sync Folder' and select that computers 'My Documents' folder.

Basically, when creating a sync like this do I make the NAS folder the main folder that the computers sync with?