i'm going to ask a dumb question related to the post above. If you get the deep signals i'm assuming that means they will be quieter but will they register the same number on the screen that they would if they were higher? i guess what i'm saying is, will a quarter ring up the same at 2 or 4 inches that it would at 8 inches on the screen but just have a fainter tone?
Not a dumb question at all.
Yes, the number can lower a bit due to depth. Eventually, you won't get a reading at all if the information doesn't make enough sense to the detector to wager a guess, but you will still get a mid-tone (usually).
If you're able to get the coil precisely over what appears to be a deep target you can try a few things to get a VDI reading, or a better VDI reading.
Waggle quickly and tightly over the target as close to the ground as possible. Turn up the sensitivity a notch (if it isn't maxed out) even if it gives you a little EMI noise. That'll sometimes push the VDI up a few points. Or, you'll get a VDI reading where there wasn't one previously and decide what to do next. That's more useful with the numbers in the nickel/pull tab range than anything over 70 because I'm going to dig those anyway.
Test the concept out for yourself with an air test. Default pro zero mode with nothing discriminated or notched out. Turn down the sensitivity two notches.
Put a silver coin on the ground and as accurately as possible start lifting the coil an inch at a time while swinging at a slow speed. (The speed you'd need to find a deep coin-sized target.) What happens to the VDI and tone as you slowly get farther away?
If and when the VDI reading starts to lower, what happens if you keep at the same distance, but waggle quickly and tightly over the coin? What happens if you increase sensitivity?
Turn down sensitivity and waggle slowly again and get farther away until all you get is a tone and no reading. Does the tone sound the same as it did when you were an inch away? What happens if you waggle quickly. Increase the sensitivity? Do you now get a VDI reading? Does the tone change? Is it the same as when you were a few inches away and swinging slowly?