The question is not about any precise measurements, just for the lack of a better title.
Trying to model what one of those non-contact voltage detectors would see when brought closer to a live wire.
In my understanding it should see an increase in the amplitude of the capacitively coupled waveform of the mains frequency because the closer the 2 conductors are the greater the capacitance.
Now when touching a metal object (e.g. ruler) with an oscilloscope probe it registers a mains frequency waveform. I would expect that if I get the ruler closer to a mains wire then the amplitude will increase, but it doesn't happen it actually decreases and increases when I move the metal object further away.
I guess there may be other factors at play like the fact that the oscilloscope is powered from the same mains (tried isolating it with a transformer but this didn't change this behavior), the mains has no ground wire etc.