Hi, I gave your code a try and it works just as the images you linked above show, but if you look at your makeGraphic call for the background, you're creating a background that's the same size as the target resolution and then drawing it at 0,0 so there is no centering needed.
If you replace the makeGraphic call with a loadGraphic call and use a bitmap image that's larger than the target res, you'll see that it's not being centered in the way the blog post I linked to above describes. It's still just drawing it at 0,0.
Maybe we have different expectations. I found a blog post for a Unity plugin here that does a much better job of explaining what I was hoping your code would do.
Give it a quick read and see if we're talking about the same thing.