Can not setup open directory due to host name
That "what I expected" part seems wrong. 

LocalHostName + &lt;your domain name&gt; should equal HostName


so, if HostName is myserver and your domain is sample.com than
LocalHostName should be "myserver" and HostName should be 
"myserver.sample.com".

In a terminal, 

dig `scutil --get HostName` 


should return the IP adress of your server.