1. People who have a reverse DNS entry for their IP address *and* whose DNS for that domain matches the original IP address, receive a partially masked host where the first part of the domain name separated by a period/full stop is masked/hidden.
2. People who do not have a reverse DNS entry *or* whose DNS does not match the original IP address have a masked/hidden IP address as their host when you /whois them. IP address masks are (almost) always fully hidden.
Since your ISP determines whether you have a reverse DNS entry and whether your reverse DNS matches your DNS, there is nothing you can do about this.