Calibre on Synology

I followed the steps for COPS (Calibre) on Synilogy. As it is advised, I placed the books on the NAS drive, created a Calibre lybrary on a PC (Mac in my case) by mounting the NAS drive (as SMB) and adding the books. After some tries and steps from the forum, I got it working. But... When I open a book in the Lybrary and try to view/download it, it tries to find a file located in var/cops/download/... and the books are under var/books/.
What has to be changed in the settings? Or does the database have to created in another way?