I thought it was a line of sight deal. As in if you have ez-pass behind your r/v mirror or otherwise out of your line of sight it is ok. kind of along the tinted area at the top of the windshield. Or when there were inspections there were guidelines on windshield damage based both on size and location of damage. IIRC up to a 1” crack/chip was allowed but it could not be in the line of sight – as in it had to near an edge.
edit:
From
http://www.ezpassnj.com/static/faq/tag.shtml#how
How do I install my tag?
Properly installing the interior E-ZPass tag in your vehicle is easy and essential.
1. Clean and dry the inside of your windshield around the rear view mirror.
2. Without removing the mounting strips from the tag, remove the tape backing from the mounting strips.
3. Turn the tag label right side up facing you. Adhere the tag inside your car to the upper center portion of your windshield, behind the rear view mirror at least one inch to the right of the center support of the mirror and at least one inch below the top edge of the windshield, or below the tinted section of the glass.