Custom base URL for assets and storage (PHP behind a proxy)

Hi, I’m running a PHP74 server on and proxying it to the outside world to my domain
However, while the admin GUI seems to mostly work, images are not loaded, because their src addresses start with instead of my domain name.
I tried changing base_url in config.yml and COCKPIT_SITE_DIR in .env to my domain but that doesn’t seem to be it?
Does anybody have any idea on how to do this?
Thanks in advance