Anyone have issues ground balancing the 10x12 wide scan coil? On my Tejon it appears to GB fine but move a few feet away and I find I have to turn the GB knob up to one full turn to bring it back into GB. On the stock concentric coil and the 5.75 concentric it takes only 1/8 to 1/4 turn of the knob to achieve the perfect GB from place to place here with the low mineralized soil in northern Ohio. The issue is most pronounced when going from dry to moist soil requiring a full turn or more of the knob to GB the machine. I'm careful not to GB it over any metal, the concentric coils GB beautifully, this wide scan is all over the place. Any suggestions...