Truckracer;
The received signal strength has to be well above the on frequency noise floor or all bets are off even for 2.4 GHz.

That used to be the case but not with SS. The signal can be as much as 40db below the noise floor and be detected.
This is the reason we need only 100 mw to do the job we needed as much as 2W to do the job on 72 even though the path loss is much higher on 2.4 than it is on 72. Check it out.