Correct, but is the web server you're trying to monitor require a host header? E.G. What do you get when you try to access the website via its IP address instead of its name?
For example. If you do a reverse lookup on whitehouse.gov you get "23.222.164.225" as it's IP address. Go to http://23.222.164.225/ however and you'll get 400 error because the site requires host headers. To access the site you must use the host header "whitehouse.gov", which is the same as typing in http://whitehouse.gov into your browser.