Bart is right, I've run air-tests and empirical tests in an iron infested site.
I switched back and forth between two identical programs with a difference of only reactivity.
Reactivity of 2 and a reactivity of 4.
The program with reactivity4 was twice as noisy.
Gave a much smaller footprint on the target, reduced depth, and never found anything that the program with a reactivity2 found.
Reactivity2 falsed a lot more on the iron but revealed more good targets in the iron that reactivity4.
I had some iffy signals (not deep) that the reactivity4 told me was nothing. I dug them and revealed a non-ferrous target
along with iron. I would have passed on it in reactivity4!
I reached for my cell phone to document the results before I dug the target to share with the group, but realized that I left my phone home.
(I know....sounds like "the dog ate my homework", but its true.)
Here's my altered program that I call "deep coin".
Sens 95 (lower if in a noisy site)
Freq. 12KHz
Reactivity-2
Iron volume-3
Target volume-4
Disc-5, 3-Tone, 0-5/6-49/50-99 are the set-points
Everything else is default.
A non-ferrous target in iron will often give a reading above 10 and under 95 but sometimes you have to go on how it sounds alone.
There is a discernible difference when a target is in the iron, even when the VDI tells me its only falsing. Two such signals were IH pennies.
I dig way too many false signals but that is because I want to make sure. I have been wrong on a few signals that I thought was iron.
Digging a plug/hole will often disturb or remove the iron and reveal if it's a target or not.
Occasionally vertical nails and some large iron will give a VDI impression of a non-ferrous target also.
So far I have found a few deep targets but nothing in the midst of iron infestation.
I did this testing because I was worried I was missing targets with my program in iron. I am now convinced that it is the best choice for my soil.