Hi tommyg,
I guess nothing may have been picked up yet due to maybe the Sussex Police or Kent Air Ambulance not transmitting a Mode-S signal. This would tie in with the fact that you are able to visually see the aircraft in question, st the time but your RB isn't.
Another possibility could be the line of sight of your RB attenna. I seem to have a similar sort of problem which is this; I live on the flight paths to London City Airport & Biggin Hill, there must be at least a hundred or so flights that pass me overhead, virtually all I can see visually & even read the aircraft reg's as they pass over my house. Many seem to be private/business jets, but what is strange is the fact that many do not show up on my RB as they pass overhead, which I find strange.
Again either a good few don't transmit Mode-S data or my RB antenna is not picking anything up till the aircraft has a better line of sight to recieve the signal.
Anyone any ideas?
SteveR