We used to use one for France but the Italian Telepass has now gone international so I sent the French one back.
I made a velcro strap and attached it to the top of my sunvisor so that with the hood down it could face forward above the screen. With the hood up it pressed against the hood material but it always worked.
The new Italian Telepass is similar in size and form and I have it attached to the windscreen on its mounting clip just behind (or should that be in front

) of the mirror. It always seems to work so I'm happy to leave it there.
The only thing is to remember to hide it somewhere out of sight if the car is parked with the hood down.