I've got to chime in on this one. I am a relative beginner at this hobby, having just started seriously this year, with the V3 being my first heavy duty metal detector. I agree with all that has been said about learning the machine. I have been getting up early to hunt parks before work, and trying to spend at least an hour a day hunting with it. I'm not "one" with it yet, but I'm getting pretty confident in predicting what's under the coil before I dig it up.
All that having been said, I routinely find coins at 8" or better. I know this to be the case, because the blade on my digger is 6" long, and the handle another 7", so a total of 13". So if I have to dig much past the initial plug, I'm over 6", and if I have to go for a bigger shovel, I'm over a foot. I have pulled several wheat pennies from 8" or better -- at least one of which was standing on edge in the side of the hole at that depth. I pulled an indian head penny at about 14" (had to get a bigger shovel for that one), another indian at 10", and just yesterday a little earring at 7". I've only found two silver dimes so far, and both of them were about 6".
In all but a couple of those, the VDI and target ID were dead on -- even that 14" indian head was a solid "penny" signal. The only times I have failed to get a good signal were an indian head penny that was in the same hole with a big nail (the VDI was bouncy in the mid to upper 40's), and a hole that had two nickels in it (a 1940's Jefferson and a 1912 V nickel -- VDI was bouncing all over from 10 to 30 on that one). Other than those two, all the single coins I've dug have been rock solid signals, regardless of depth.
I tend to run a tweaked "coin and jewelry" program most of the time. I have the discrimination sensitivity cranked up to 90, the all metal sensitivity at 70. The ground filter is on 10 high (which I think is the default). I run the gain as high as I can without it falsing too much. That deep indian was with the gain at 13. If I'm at a location which gives me a lot of falsing, I'll turn the gain down first, and if I have to drop it below 6 or 7, I'll starting bringing sensitivity down too.
BTW, All of these were with the stock 10" DD coil. (I have the 5.3 and the super 12, but haven't used either that much yet.)