Can the F70 Go Deeper than 8" on Coins?

I have been using my F70 equipped with the 11"DD coil for the last 13 months. I use SENS 99, THRES+9, 2F tone and only three DISC settings 0,6 or21 depending on the my noise tolerance for the day. I have fairly mild soil here in Illinois. I have never found any coin deeper than 8" and only two at that depth. Most are in the 6"-7" range and hit hard but they are usually from the 1940's or so. These are sites that should have older coins so I keep think I should be finding deeper target. My 8" coins were IH and ID'ed in the low 40range. Is there anything I am doing wrong? I put in alot of hours so I think I should have put my coil over some dep silver by now. I have systematically worked a grid over fully 1/3 of this park I am working and still no deep silver. GB is in the low 40's at this park.

I have been using my F-70 about the same length of time I find coins all the time at 8,9" (dimes) quarters 10-11" half dollars-silver dollars 12" sense 99 disc 0 (gain) 5-6 3H--4H in 3H-4H tone it will let you know it there is silver under your coil, I hunt in Tone only, dig high tones don't look at the screen if you get a high tone walk around the target while sweeping the coil use short sweeps like the minielab wiggle to isolate the target, my soil is 65-68 with 1 and 2 bars on the FEO gauge, a setting of +9 on the gain maybe too much, over 6 is over driving my detector, I have a real world silver test
garden silver all different depths 8" dime is the shallowest I have planted. before I go detecting I sweep my garden to check my detector before I leave, I have never been able to run my gain past 6 if I do I cant find the 8" dime worth a hoot. HH

Find a VERIFIED CLEAN patch of dirt.........and bury a dime at 9".........and you will have your answer! ((( Don't be disappointed ))). I had your problem in Itasca/Chicago a few years ago.