Lets say I am doing a review of a file that is pretty large (whether I expanded it, or the diff is just large for some reason) and I scroll down ~200 llines, if for some reason I don't know what file I am in already (eg I did a "find" to find a method inside the file) it is annoying to have to scroll up and see what file I am in.

I think the ideal solution would be to put a sticky bar at the top of the page when you scroll past the header of a file you are reviewing so that even if you are 200 lines down you know that you are in some/path/hello_world.php.