If you are facing the car, top right side. IF you are inside car, top left corner. This to steer away from wiper path but not to put close to metal pillar or metal part of the car like >6cm away.

Probably your glass or headlamp is oily or not cleaned properly. I washed my car with water-jet cleaner and the RFID is still there for more than 3 years

Got people just stick it behind plate number. No one can see and safe from road gravel and washing as long as your plate number sticker hold

The main problem is that the transmitters at toll both are not all the same in transmitting power and positioning.

This is what I told them. In the beginning they claim can go through faster. Certain place slower than walking also failed. Then I told them that, they just said sorry

Mostly transparent and the shadow part the light get refracted and it was just like nothing on the headlamp.