@dumpsterqueer@ondergrond.org @petrichor yeah, it works fine:

required mastodon config:
LOCAL_DOMAIN=pixie.town
WEB_DOMAIN=social.pixie.town

nginx config for top-level domain:

location = /.well-known/host-meta {
return 301 https://social.pixie.town$request_uri;
}

location = /.well-known/webfinger {
return 301 https://social.pixie.town$request_uri;
}

subdomain that hosts web just has the default mastodon nginx config, no changes neccessary