This one really frustrated me, I switched from HellaNZB to SABnzbd (after many years of loyalty) so that I could start using SickBeard. When it came time to configure where my downloaded files end up I found I could only change the last part of the file path and the root, or the base folder, seemed to be hard-coded. My first thought was just to enter a full path in the box so I entered C:\Users\fettesps\Downloads and got an obscure error so I figured it couldn’t be done. After some serious Googling I found a forum that suggested reversing the slashes and dropping the colon, which worked for me. So enter the full path, completely ignoring the idea of a base path, but enter it like /c/Users/fettesps/Downloads/ and you’ll be good to go!