think of this feature as a “suppressor” of iron. On one hand IB prevents iron from reporting and assists you to “see” a non-ferrous target lying next to iron.
However too much of this “suppressor” and now it starts to hide / mask the non-ferrous as well.
Am I saying not to use it? Absolutely not. Everyone has different goals when hunting. Preference if you will.
My goal was to learn and operate at F2 - 0. At first I dug quite a bit of iron but as I learned what iron sounds like with no iron bias, I started digging less and less. I still dig some iron when I go out however it’s minimal and (to me) a necessary evil to dig suspect signals.
I have done quite a bit of testing on actual in-the-field coin targets while adjusting iron bias over them. My conclusion is to use it sparingly. It’s a powerful feature that can help and at the same time hurt if too much is applied.
I have heard coins partially masked and as I raised the iron bias ( only a few points) it made the signal degrade to where I would of walked right over the coin. The best way to understand IB is to get out in the field and adjust it over Non-ferrous targets.
good luck in the field !