Oldtown, what you are saying is very hard for the purist relic hunter type to digest. If they hear someone say they've "tuned out foil" or "passing up tabs", they will absolutely bristle, and consider you a rogue beginner. These are the hard-core types who've primarily hunted CW or rev. war type stuff. Or beach hunters, etc.... Afterall they reason: "you might miss a gold ring or rare button that reads down lower", etc...
I even hunted with a dealer before, who ..... like this ..... was quite adamant that you should never pass low conductors, because ........ otherwise you'll miss small gold, nickels, etc... It made absolutely no sense to him, that anyone would foolishly pass lows, since it was/is so easy just to dig it all, and thus, not miss anything. Ie.: "anyone without the patience to dig some junk, is obviously 'missing out', etc..."
But the reality is, that by the end of the day, in junky inner-city urban parks, these purists will end up with an apron full of junk, and look with envy at your silver coins. They can't understand why they don't have an equal amount of oldies, since afterall, if they're digging all, then they should have the "best of both worlds" right? But the reality is, they will spend all their time digging shallow foil, tabs, etc... It simply isn't worth the occasional cruddy orange buffalo they will find, and the gold ring per hundred aluminum items, to be divoting up the park. You will simply, at some point, be better off going to a swimming beach somewhere (where ratios are better) if jewelry is your goal, and NOT trying to strip-mine turfed parks.
It's kind of like playing blackjack: When you have 20 in your hand, do you take another hit, or do you hold? Of course you hold right? EVEN THOUGH that next card *might* be a one card. Why not take another hit then, if the next card *might* be a one? Because odds are, it's not going to be a one. In the same way, in detecting (junky parks anyhow), there are times you "hold", and go for the known better-odds factors.
If you're in an area that allows strip-mining, by all means do so. But in other situations, we need to be a little more picky.