I had mine inside for most of the testing at manual 20, found accurate id at 10 inches and degrading id's as you headed towards the 11 and 12 inch mark. I went outside and tried it at manual 25 and was getting closer to 14 or so with degrading useless id's at the 16 inch mark, basically the detector knew something was there but that is about it. As I have noticed before with the higher sensitivities and longer distances between the target and the coil, a much faster "swing" will get you more "depth". Try it, keep swinging a target past the coil until you can barely hear it and then swing real fast. You'll find a renewed and likely id'able signal.
Now, we all know these tests are a long way from real world situations, but I believe it gives you an idea of what the machine and coil are capable of, and I highly doubt the real fast swing will work in most of the parks and yards that people detect. For me though, detecting in a field with barely any signals for most of the time the faster swings work for me and if it does get me an extra inch great. Of course as I get closer to the homesite I have to slow down since like anyone else I may miss something amongst the trash Sorry a bit off subject at the end here..
Happy Hunting