i'm new to detecting. i've had the xlt for about 3 months.the deepest targets have been a 1858 flying eagle and 1905 dime at 7'' down. can't get any deeper. i read a post here about the dime air test. the detector is about 6''. the post read about checking ground from the power box to shaft . he stated he then air tested a dime at 9'' with slight signal at 11''. this box is grounded. any help would be great. tom in cinti.