super sorry to post this as an answer where it is actually a question, but my reputation seems to be too low for writing comments.

I configured my signal proxy just like you, but I do not get a connection. With standard ports (80 and 443) all works fine unless I'm in the same network as the proxy but that's another story. My question would be how do you configure the proxy settings in the signal app? How do you set the non-default ports in the app? my-super-signal-proxy.de:44443 did not work for me.

Thanks