Testing new 13" Detech coil on the T2

[Qball]

Received a new Detech13" coil for my T2 this week end I have been experimenting with it on the test track and have found an interesting effect that I hope some of you might comment on. I placed a half dollar in a 12" hole and passed the coil over it with the coil held close to the ground and received no signal. Repeated the test with the coil held 4" off the ground and got a great signal. Does this coil need to be elevated off the ground for best results or am I just nulling out surface iron noise by doing so. either way it seems to work. My soil is not particularly mineralized. Thanks,Qball