Just solved this issue.
As it might help another lost soul in the future, here's how I did it:
The key to success is all in the EXPORT function.
I made up a little export script, that would drop a file with an odd name to the DocumentsPath folder.
After I ran my script, all I had to do was to locate the odd name from the terminal - and I was able to find the specific document path that Filemaker Server uses on my machine!
Little trickery - and you shall prevail....