I have not been able to have my transponder for EPASS to work through the windshield mount. I don't know if the glass is a special glass, or the sensors interfere with the signal. I brought one back to IPass (Illinois Tollway Customer Care) and they said that the one I had worked. But when mounted in the car it doesn't. Is there a preferred place for the transponder to work in the windshield or will I need to get a license plate mount?