It looks built-in CODE doesn’t take into account tweaks applied to NC… somebody reported this issue shortly (don’t have the reference handy)…
I have no good hint for built-in CODE… as your are using Docker and Reverse Proxy you could easily setup regular Docker CODE image which is more mature in my eyes. And you definitely have little more control over moving parts of the installation.
Take a look here for example with docker and traefik - should be not hard to adopt for other RP.