Connect to RCS behind proxy, tls issues

Hi, we have a setup where the Remote Connection Server is running behind a reverse proxy (Caddy). The RCS is configured without TLS, which is instead handled by the proxy.

Now, I am able to connect to Deadline from a workstation. In the connection settings, I select “Use TLS without Client Certificate”, and I pass the ca root cert.

However there is a headless client, which I cannot get to work. I tried all sorts of combinations of installation parameters. As you can see, it is trying to connect to http://deadline.cairos.corp instead of https:// which I think is the cause of the problem. If I enter https://deadline.cairos.corp as the proxyrootdir, it tries to connect to http://https://deadline.cairos.corp.

Which option am I missing? It is a bit hard to tell which are the client options, and which the rcs options, since they are in the same installer.
I tried with enabletls both true and false, did not help. I tried passing proxycertificate etc. etc.

I verified with openssl s_client that the connection works from the same host and the handshake is successful.

ERROR: UpdateClient.MaybeSendRequestNow caught an exception: POST http://deadline.cairos.corp:443/rcs/v1/update returned "One or more errors occurred. (Error while copying content to a stream.)" (Deadline.Net.Clients.Http.DeadlineHttpRequestException)
ERROR: DataController threw a configuration exception during initialization: Failed to establish connection to deadline.cairos.corp:443 due to a communication error. (Deadline.Configuration.DeadlineConfigException)

Edit: here is an example installation command

$installers/DeadlineClient-10.3.2.1-linux-x64-installer.run \
    --debuglevel 4 \
    --mode unattended \
    --prefix /deadline10/client/data \
    --proxyrootdir deadline.cairos.corp:443 \
    --cacert /deadline10/client/deadline-root.crt \
    --connectiontype Remote \
    --noguimode true \
    --enabletls false