Yes, the odds say you have almost surely passed up gold rings digging only high tones. But...
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From the numbers I've seen, between `the zinc, foil and nickel ranges, you get about half the gold rings. If you are only digging high tones in the 3d enhanced mode, you'll be getting a good chunk of that half but not all since the lower end of foil and the upper end of the nickel range don't hit in high tone in enhanced mode.
Only you can decide what your level of patience is. And what the probability of gold is where you are detecting. A typical front yard is going to have a lot lower gold probability than a tot lot which is going to have a lot lower gold probability than a beach.