You know I think its your spot , I have a very deep machine, the blisstool, and in the same kind of spot you have I cant get much depth because the nails are so infested, it only takes a small nail to mask a target , so cranking the gaine is a no , no use less gaine and a smaller coil or just dig the nails , you may have coal ash this probly does not help . my advise hunting with it would be small coil, lower gain dont go at it super tuned , use short sweeps in both derections, this may bring somthing out for you , and last of all dig out the nails I did this with my golden umax, and it worked after removing a nail, suddenly a high tone came thru it was a merc dime somtimes the only way to beat nails is to ingage them and remove them . hope this helps some Gunnar