Not really a big deal though because I was rotating the camera to see my mirrors, but with the proper setting you can get both mirrors in view. I don't think the camera zooms out though, I thought it just panned left and right.

Does Forza not just render the whole cockpit at all times anyway for rotating the camera? And this just moves the view point back further? And can you not see less outside the car when you move the camera back from the windscreen?

It does, but when you use the technique described in this thread to get the POV to back, the game assumes you are using mulitple monitors, so rotating your main screen doesn't make sense because the left and right monitors would be having those viewpoints.

It doesn't bother me when im in cockpit view.