I'm using an Exp. II with standard 10.5" coil. That is probably similar, depthwise, to your setup. My experience on beach depth, for coin-sized targets, both dry and wet sand (assuming nothing wickedly mineralized or some other issue) is:
- About 9" (maybe 10" if I pushed it) and still get reliable TIDs to tell highs vs lows, etc...
- Up to 12" if I'm willing to chase some where I have no idea of conductive vs non-conductive. Usually if I scoop some out, and re-scan it after scaling back some sand, then it comes into the TID range.
- Up to 14" on coin-sized targets if I'm in sand that allows me to go up to 25 on the sens, and am investigating flutters that BARELY warble the threshold. In those cases, sometimes it's been my imagination, and there was no target. But other times, as I pull 6" off, and re-scan, there's a signal that comes into range.
But realistically, on coin sized targets, about 12" is max, if you're willing to for-go some TID on that last inch or two.