You should scrape the places that you don't want it take over. I have almost decided to conced the battle a little and only keep my front glass clean of coralline.
One thing that I found works very well for glass tanks is actually a glass and tile scraper. They come with thicker, stronger, replaceable blades that do the job well.
I started out using a Kent scraper on the long rod. First the rod broke after a while, and then the flimsy little blade would bend over at the corners, I would put a new one in and bend it in a matter of 2 weeks or so. That is just my experience and your results may vary.
