Can Mozilla VPN users connect Mullwad servers directly?

I've tried to fix my IPv6 compatibility issues by using Mozilla VPN over NAT64 box this way.

I've tried to improve this setup but it did not work as expected. 

Mozilla VPN uses Mullwad internally and we can find Mullwad's server name using this interface. Just fill "us-nyc-wg-505" in hostname field and after that you will see something like: "us-nyc-wg-505.relays.mullvad.net".

With this information on our hands we can replace:

Endpoint = x.y.z.y:23662

To:

Endpoint = us-nyc-wg-505.relays.mullvad.net:23662

Sadly in my case this trick did not work ;(

If you have any advice about ways to fix it please share.