When I got my new sticker decal type EZ Tags that replaced the plastic modular tags a month ago, here in Houston, I was concerned about the same thing. The shaded area behind the rear view mirror is called a "third visor" by the windshield glass industry, I guess because it acts like a, you guessed it, third visor in addition to the two inside your car that you can flap down or against your side window. I called the EZ Tag people and asked iif I could stick the new tag on top of the third visor and was told that there was no problem. The person that helped me, interestingly enough, did advise not to put it on top of the shaded area that goes all the way across the top of the windshield. I placed the tag on the third visor and haven't had any problem or contacts by the toll road authority in the 7 weeks since I did.