@bookreader1: Last edited by NiLuJe; Today at 05:15.
That didn't help ^^.
To answer your original query (I think?), even with an sshfs mount, the 'folder sync' handling of Calibre is fairly generic, and doesn't do any of the kind of special hand-holding needed to Do The Right Thing (like the Kindle driver does), so it's not a terribly fruitful angle of attack. It works for the basics, but that's not a complete solution, IMHO.
Short of trying to handle that on Calibre's side by making folder sync smarter, you're left with other basic solutions like rsync, opds, or custom syncing scripts (f.g., Librarian). That, or implementing the protocol used by the Calibre Wireless Driver (which I think
KOReader does, to a certain extent, but, again, in a device-agnostic way, because KOReader doesn't need any of the crazy extra stuff the Kindle framework does).