Redirect & URL issues

Hi everyone,
I purchased this domain for reverse proxy purposes for my home server. I would like to input a URL for my subdomain and have it redirect to various self-hosted containers. I suspect I have this configured incorrectly on the domain side and would like some guidance. 

I've set up various CNAMES for my server applications: for example, radarr.mortnz.com, pointing at my DDNS on mysubdomain.duckdns.org

Then to create the subdomain on my domain; I've gone to Domain Forwarding and created:

Forward from: radarr.mortnz.com

Forward to: mysubdomain.duckdns.org

I expected this to then create the subdomain and redirect with the CNAME to mysubdomain.duckdns.org with the URL remaining as radarr.mortnz.com; however the URL changes to reflect the duckdns.org URL and some of the forwards don't work at all. 

Would love some guidance!