Finally today, XenForo 1.3 has tweaked the censoring system to give you more control. Primarily, this is designed to workaround the "Scunthorpe problem"--you should see the issue right here until we roll out 1.3.
I see how you've done this, just matching on the word on its own. However this won't censor the word ending in - head... Seems like a whitelist is still needed.