Hey! I think you may just be over analyzing the car, which is easy to do when test driving. I remember noticing it once, and haven't thought about it since. A bunch of the technology that runs some of the safety features are packed away in that area by the rear view mirror. I think you'll find that most cars with all the features have a similarly sized box behind the rear view mirror.
For what it's worth, I wouldn't think you'd notice it after the first day or two of driving it.