How to make rootless podman container appear to be on its own IPv6 subnet on the internet?

I am starting with podman (rootless) and I have configured an Ipv6-only subnet with
podman network create --subnet xxxx:xxxx:xxxx:5401::/64 --gateway xxxx:xxxx:xxxx:5401::1  podlan6 where my ISP gives me a xxxx:xxxx:xxxx:5400::/56 prefix and my host has an IP in xxxx:xxxx:xxxx:5400::/64.

When I do
podman run --rm -it --net=podlan6 --ip6 xxxx:xxxx:xxxx:5401::10 docker.io/curlimages/curl -6 https://ip.network, I see that the container appears to the server on the internet as xxxx:xxxx:xxxx:5400:yyyy:yyyy:yyyy:yyyy (my host’s IP).

How can I get it to appear as being on the 5401 subnet ?

podman is 5.7.0 on Ubuntu 26.04 and the backend is pasta 0.0~git20260120.386b5f5-1.