You should place the Transponder as near the front of the machine as possible - on a solo one of the best places is on the top of the fork leg. On a sidecar the best place is on the chassis next to the sidecar wheel.
The Transponder needs to be vertical i.e. you need to be able to read the number when it is fastened in the mounting bracket.
The bottom of the Transponder needs to be pointing to the track.
If you are not sure please ask at Technical Control - They do not bite (well most of the time anyway)