Relevance language is designed to query the local machine’s resources in order to increase the safety of the language. The fact that you can use the relevance debugger or QNA to check a file located on a remote workstation using a URL is a side effect and not by design. If you try that in a fixlet, task, analysis or retrieved property it will fail because the BES Client runs in the system context and usually does not have access to network resources.
My suggestion for what you are attempting to do with the relevance debugger is to copy the QNA folder to a network accessible location, use remote desktop to open a session on the machine you want to check then run QNA in that session to test it locally.
The other method would be to use regedit to connect to the remote machine, export the registry keys then apply the exported .reg file to a test machine that you can run QNA on. I prefer the remote desktop/terminal server method myself.
As a side note, have you ever tried to get regedit to open and automatically connect to a remote computer using a script, command line parameters or other automation? I looked for a method a few months back but never did find a way.