After installing LogHostname there are no specific rules or changes that need to be made for it to start working. The easiest way to test the filter to make sure it is working properly is to go into the monitoring->logging tab and logging all "web proxy" traffic. After this (if the filter is installed) the right-most column, "URL" will display items of the form:

http://yoursite.com/etc

If the filter is not working it would display the URL in the form:

http://1.2.3.4/etc