Why fly over the top of an airfield anyway? We have reviewed our procedures after a student(not one of ours) flew into another aircraft O/H Moreton in Marsh disused. Since then we/I always try and use checkpoints we think others may not be using!
Also dont forget if there is traffic in the circuit the radar controller may well get a scrambled picture as you go into the overhead and may not be able to differentiate between you and other aircraft.
My advice stick with radar but change to advise the AFISO of your intentions and then change back to radar.