Modified from a post I made concerning water detecting over iron rebar.
I was thinking about using the HF sniper on the 305 and turning the sens down too. I bet the iron sporadically supertunes the vlf detectors, just like the supertuning trick on the Propointer. So the very lowest sensitivities could prove stronger than what I might think. Depending on where the good target is in perspective to the iron it could actually make the good target easier to detect at the right sensitivity. This is probably part of the mechanism behind falsing.
This might mean that when detecting around iron poles at a playground, rebar, etc, if you go around the same pole multiple times at different sensitivities you might find different pieces of metal that you would not find at different levels of sensitivity. It might be a 2 or 3 out of 10 that finds the gold ring and not just the lowest or mid sensitivities.
You could find a quarter at sensitivity set to 1, then go back over with sensitivity set to 3 and miss that same quarter due to falsing/halo, but find a ring that is deeper and an inch further out from the pole, because the iron pole is supertuning the your detector just right, from just the right angel. (Angle not angel, lol, must have been thinking about halos, lol!)