Example of plugin configuration:

[
   @gerrit(gerritProjects=[
         {
            branches=[{compareType=PLAIN, pattern=unstable}],
            compareType=PLAIN,
            disableStrictForbiddenFileVerification=false,
            pattern=dev_manifest_project,
            filePaths=[
               {
                  compareType=PLAIN,
                  pattern=some_manifest.xml
               
               }            
            ]
         }
      ],
      serverName=gerrit.internal.com,
      triggerOnEvents=[@refUpdated()]
)])

Found info in old thread:

Feb 24, 2014. When there is ref-updated the option to choose path is taken under consideration. It just not working for ref-update.

Oct 15, 2014. I can't see anywhere within the plugin's documentation if this is a bug or an expected behavior. "Ref updated" doesn't care about specific paths or topics.

Nov 11, 2014. On the contrary, when you use ref-updated, there's no information about the changeset, so it is not possible to check for file inclusion.

If this is not possible to fix, then at least these restrictions should be reflected in the documentation.