Using a horizontal bar to denote vertical position is a tad unintuitive. I feel like this doesn't really solve the problem you are talking about, and instead adds to the confusion of readers who notice the bar.

Edit: Keep in mind that as I'm reading the story, my eyes are nowhere near the top of the browser. If you want to give me context, the top of the page is not the best place to provide it. It does make for a cool demo though.