BOSH URL should be based on FQDN, not XMPP domain.
For BOSH / HTTP Binding, various URLs are being composed. These URLs are primarily used on the admin console, to show what the connect endpoints of BOSH are. An example of this is:
The domain part of this URL is taken from the XMPP domain name. The XMPP domain name, however, has only meaning in XMPP-context, and need not be resolvable through A or AAAA records (which are used by HTTP). Instead, the fully qualified domain name of the server should be used.