The "Uri b.s." that you refer to has nothing to do with your problem. According to the .net documentation UrlReferrer "Gets information about the URL of the client's previous request that linked to the current URL." This is not what you want. It's coming up null most likely because you are typing in the test url directly and thus no referrer is being sent to the server.
What you DO want to look at it is
UserHostAddress which "Gets the IP host address of the remote client".
Peter
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Work smarter, not harder