I don't do much relic hunting anymore. When coin hunting I still listen to the audio response and use the target Id screen as a back up to eliminate the need to make extra holes in a lawn.
In this case target ID to 8" is good enough. If there's an inkling that a target is good, no matter what the meter suggests it might be I dig it. So I still dig tons of trash. Now I do find many modern machines
that have good depth, good screen target Id and good audio saves me a lot of pain from having to dig a lot more ( many ups and downs) at the end of the day. Usually feel it the next day.
I also find these days I mostly hunt in all metal mode in 2 or 3 tones. Where many screen ID machines fail when a good target buried in the ground is ID'd as trash, mineralization will drop target ID numbers.
Ever bench test a screen machine and it ID's correctly air testing, then you go hunting and your just not finding anything good? Then take a non-metered machine, let's say a Tesoro and you start finding coins everywhere while hunting in disc. mode. I considered Tesoro detectors one of the best Beep and Digs for Canadian clad coin hunting, metered detectors like to classify them as junk and or with very bouncy target ID numbers. As long as you set you Tesoro disc just above nails, you'll find them all, they can't escape a Tesoro.