Just got my coil replaced by Minelab and was out in my coin garden checking it out. I noticed that I get approximately 2 inches more depth in ferrous coin than in low trash, high trash, or ground coin. My coins are 4 to 6 inches deep and I water daily. I was lifting the coil to see how much I could get and I could get 9 inches with ferrous coin and 7 with the other three. Has anyone else ever checked this. Just curious.