EM Plate conductors are 2D sheets. That's as complex a shape as...

EM Plate conductors are 2D sheets. That's as complex a shape as the EM modelling software can handle. The 2D sheet quoted in any model is the theoretical sheet that best mimics the real world anomaly when used to calculate a model response.

What complicates the issue is that real world conductors are rarely of ever sheets. Blobs, cylinders, ragged patches, you name it but rarely sheets. Also, the EM anomaly response is only that part of the real world conductor that couples well with the transmitter signal from the transmitter loop to induce a current in the target, and gives a response that couples well with the receiver to be able to measure it. In the bad old days of single component receivers this meant conductors could be missed. With theee component receivers it's still a bit of an issue but not too bad.

So the 2D plate is the best effort any geophysicist can do to calculate a model for the real world conductor given all these factors.

Clear as mud?