em results - late channels

Hi,

Just wondering about possible interpretations of "late" time channels in EM.
I am looking at some diags and the notes mention the late channel relates to the potential depth of the EM target.
But I also thought late channels could relate to the conductance of the EM body, basically strong back EMF/eddy currents stretching out the EM field decay time.
How do the geos work out whats the likely cause of late channel results. Is it as simple as working out the time for the EM field to travel a certain distance and if the late channel is longer than the field depth penetration then its due to inductance effects?
Or is my understanding of EM complete BS :-)