While I don't know if that is true or not because I don't watch news stations all day. It is an interesting (and poor) business model.If you think Fox is to the right, then I know where you get your news. Fox has been middling left for a few years now.
Fox News, as a right leaning news source, will/would get more viewership from crazy people on the left. It is the Howard Stern effect, they basically found out that people that "hated" Stern listened longer than people that loved him...because they wanted to see what he would say next.
Fox News has almost no reason to change their format.