When hunting deep in iron you might want to try monotone.
The F70/F75 monotone and 6 on the disc.
On the T2 set the disc at 21 to take advantage of this technical information.
http://www.dankowskidetectors.com/discussions/read.php?2,2251
I hunt in some very difficult mineralized soil with crazy amounts of extra iron.
Monotone, (and disc even lower at 0 or 1), and All Metal are my most common settings and I have found plenty in many difficult and so called hunted out sites.