Got a Fisher F22 ID & depth in ground bad

It does pretty good in an air test, 8.5" on a dime, with ID 62-66. But when I try it on my 5" deep dime, the ID really varies, signal is weak in my moderately mineralized soil. If any of you have the F22, are your results this poor? Of course the AT Pro has perfect signal & ID, but I also get nearly perfect results with B.H. Land Ranger Pro and Teknetics Eurotek Pro, with no ground balance being used. Guesses anyone? Thanks!