The answer is "it depends". I sometimes (in junky urban inner-city turf) set my disc. to reject foil and (gasp) tabs too! Better than going nuts or getting kicked out of the park d/t too many holes every foot
So sometimes I angle for deep silver, and save the jewelry hunting for the beach or relicky environments.
I can still get deep silver when in high disc, but it depends on how critical you're being on the audio. If you're waiting for the "bells of Notre Dame to ring", then yes, you'll miss deeper silver or copper. It depends on the machine you're using, the audio it gives on iffy/marginal signals, etc.... Even for the person who has his screen (if we're talking about the Explorer here) "wide open" and elects to use his ears/eyes to discern what is shallow foil vs a deep silver/copper, he is still "using discrimination", to try to discern the "peaks through" of the deeper hits. A 8" deep silver dime might not peg a consistent #, verses the 3" deep silver dime. You might have to figure out where it's "trying" to hit, as it bounces around the screen
The problem with runing the disc. pattern (or knob, or whatever machine you're using) too high, is that on the off-bounces (where it bounces low based on your swing and how accurately you were over the target), you would get a null. This may cause you to keep walking, assuming it's junk. But by having your disc. wide open and relying on the screen or needle, you are allowing yourself to "double-check" any questionable hits, thus narrowing in on the exact center strong-spot.
Had you gotten a null, you'd never have been drawn to double check the spot. That's why it feels like people are getting more depth to go lower disc. You are merely drawn to double check more often. But the actual bounces up into the disc. threshold of our mind, has not changed. Ie.: if it consistently, every bounce, bounced low, we'd conclude "must be low". But if you got an occasional bounce up high, as you turned 360* around it, you might be persuaded to double-check
