Metal detector experiments.

[Koala]

Also, if you place the coin at a lower depth than the nails, you will be amazed which detectors cannot see the coin; whereas they could when all three items were in the same plane.

Yep tried that

Results with coin lower than nail also alters with a DD or concentric if swinging down the nail even with the same detector.

Very small target next to fairly large iron is almost total dependent on coil size regardless of detector. Recovery speed and so on does not come onto it. Slow recovery speed just means slower swing for the same result.