I'm suggesting that you and I, and anyone else that wants to grow in becoming a better detectorist should experiment. Air tests are fine for what they are. So are in ground test. Each provide information, but the information that is more relevant is that which comes closest to duplicating actual field conditions of the sites we actually hunt.
As far as your points in this Thread, instead of assuming that you could extrapolate from your prior Air testing, why not duplicate the actual test as best you can? I was impressed enough with the video that I did just that while at home for lunch today. Not on a Medieval Hammered low alloy Silver coin. I haven't dug one of those yet, but I do have a moderately tainted 8" deep Copper Cent. Close enough for me. Park M3 12 Sensitivity LG 30 coil=a solid, repeatable, very soft hit.
I will never need to hunt with Sensitivity that low but it is good information and gives one confidence that the machine will perform when I need to run at 20 or 16. That's the point for me. Practical field use knowledge.
Also, there is no need to be so prickly and quick to want to prove your point in so many of your Posts. We are all here to help each other if we can. I enjoy a good exchange of thoughts & ideas but am not interested in reading or participating in arguments.