You are not missing anything. I bought the 705 thinking that with a 3KHz coil, I could go as deep as an eTrac for silver dimes and wheaties, but a lot lighter. I was wrong.
I tested it in highly mineralized soil, as we have here on the west coast, and it failed to deliver. Either there is a hardware design error, or firmware error with it. As you reach near maximum depth on a silver dime, it reads +48, which is generally notched out for hot rocks. At the very limit of sensitivity (about 7.5" in my soil) a silver dime "wraps around" to -8 (iron!) on the detector. If you were to hunt with only -8 to -2 notched out to discriminate iron, a really deep silver dime would give you a negative hit! What good is that?
I've had an email into Minelabs engineers about this for a month now and no response. This behavior has been confirmed by at least 3 others in different parts of the country. I sold mine.
Another huge negative with this machine, is the lack of an 8-10" DD 3KHz coil. Concentric coils, simply cannot separate targets at depth.
George
Aloha, Oregon