@johnm
You can't separate PAW from ATOM grid and missing ATOM grid connection is much like shielded SE2.
That is probably untrue and let me explain why.
The SE2 ‘shielding’ is unlikely to give zero range detection as the attenuation generated by airframe, engine or human obscuration is only likely to
reduce detection range, not completely blank it. So let’s say that FLARM reception, the weakest signal, is normally 4nm. That signal will likely still be detectable at say 0.5nm even if there is lots of skin, bone, body fluid, engine and airframe in the way - but it will be reduced. (BTW @Straight Level that could be scientifically modelled quite easily and has been done for mobile telephone attenuation in many studies - give it a Google
).
Now, the other way around for PAW. If you are out of range of an ATOM ground station and can’t receive the OGN/FLARM uplink, it doesn’t matter how close you get to your threat aircraft if it is FLARM only [edit] - you will never see it. It is absolute, and your aircraft and your FLARM-only threat aircraft will need to move toward the ground station to see each other.
So in your above example, the air-to-air detection “fails safe” as eventually you will detect the threat the closer you get, whereas the ground-uplink detection just “fails” until you and your conflict get closer to the ground station - which unless you are flying in formation until you do, is an unlikely scenario for the latter.
PS. Here is one such quantitative analysis of the effect of the human body and other materials on 2.4GHz signals:
https://www.dataloggerinc.com/wp-conten ... uation.pdf If you do the maths, it is tricky to get down to 100% attenuation (called a Faraday Cage) and so everything is likely to be detectable, but just at
reduced range in the air-to-air scenario.