It is always a challenge trying to guess if a detector is not detecting deep. You can try to simulate buried coins, but a freshly buried coin will not respond the same way as an old coin beneath the surface. This was the case with my V3 after "trading up" from a DFX. I was not really sure if the V3 was detecting as deep as my DFX had been. My DFX had found coins more than a foot deep, with dimes being detected at 10 inches.
I finally figured it out for sure one day in my own yard. The V3 detected a dime that I had missed with the DFX. It was about 8 inches, possibly on edge. Maybe that is why the DFX missed it, but the V3 nailed it loud and clear using the 950 coil.
For more details check out the post from a few weeks back: http://www.findmall.com/read.php?66,1177219,1177219#msg-1177219