Read the stuff on Roman's web site I linked to. There is no "threshold" on a super-regen receiver; only random pulsing if no signal is being detected, or the on-off detected keying envelope if receiving an on-off keyed carrier. The only way to tell if the receiver is detecting signal vs random noise is to look at the temporal information in the detected output signal using timing or possible tone detection. Read Roman's article very carefully. It explains this very well.
The output from the receiver effectively differentiates the RF envelope from the transmitter. There is no output that is proportional to the "strength" of the received signal. If you are trying to "measure" distance between the transmitter and receiver, you will need a different kind of receiver (superheterodyne, or Tuned-Radio-Frequency).