If you have a hard time determining their IP, here's a trick that might work. Visit their site with a unique but innocuous-looking path or query that would never be accessed by a normal user. For example:

http://4co.in/?q=1

If the query string is being passed through, which I suspect it is, you can use the query string to easily locate the corresponding entry in your own logs. Or, if the query string isn't being passed through, you can use a path instead:

http://4co.in/q

You probably already thought of this technique. I decided to post it anyway in case you hadn't, or in case anyone else is facing a similar challenge.