Oh men... I'm sorry for asking this... and PLEASE, don't take this wrong... can you re do this test? Without the coin too... and if possible, showing the ID. I love all your videos related to metal detect, but there was a video that you recorded back in the days using Anfibio Gen Delta Mode, Deus with gold field and the nox that i believe you had it wrong... both Anfibio and the deus had a signal because both were running a mode that uses threshold, that's why you had a signal... (and you didn't check the soil without the silver coin). You actually concentrated alot of mineralization in a certain area, while the surrounding is mild soil.
Try use beach 2 (it uses very low frequencies, so that's why you will experience even more EMI), and see what negative ID's you get from the soil without the coin (example -9 , -8) then try with coin, if you see a negative or positive ID that you didn't had before ( for example -1 or 0 or 1) that should be your coin affected by the wrap effect (depth and mineralization acts as subtraction) and the more deep it is, the more mineralization will be over a target. Something similar as diving (the deep you dive, the more presure)
A lower Reactivity can make mineralization sound as something a target.
For more ideas, check out this video that i recorded!
I'm very familiar with mineralized soils back here in Europe.
Keep up the good work mate!