tpl debian_postfix.conf.master includes hard-coded /etc/postfix
The {config_dir} placeholder is used in the debian_postfix.conf.master file, replaced with /etc/postfix in main.cf. There are a couple instances of the literal text /etc/postfix in the settings. I have no idea if this would affect any sites. But the file was made configurable for a reason, so I'm noting that this would be an error for a site that relies on a non-default config_dir.
If approved, this can be assigned to me.