/etc/default/urbackupsrv config file is being ignored

I’m trying to setup a non-default configuration for the UrBackup dockerized version on a Raspberry pi 4b (arm64).
After some research I found that the config file is located at /etc/default/urbackupsrv and is being referenced from /etc/init.d/urbackupsrv

So I mapped a host-level file to the container and changed some of the settings. Logging into the container shows that the file is mapped correctly. However it doesn’t seem to matter what I put in that file, it just gets ignored. Permissions seem to be ok (original file and new file have the same owner). I recreated the container several times and even went as far as resetting DB, nothing works.

I’m at a loss at what I can do further, as older forum posts seem to be outdated…