Eltons right. If you sweep over a coin that is flat. you probably will get a repeatable signal. If the coin sets at an angle, sweeping towards the flat would give a tone where sweeping back towards the edge may not. Dave J (FTP engineer) says getting better depth isn't a problem. But if you're turning up too much depth, it exceeds proper detection and ID of coins/metal closer too the coil. An 8" coil can only make so much of an effective, well shaped electromagnetic field. Pushing it to do more would be like turning up a radio so loud it starts distorting sound to unintelligible levels. A good field can go 2 feet into the ground or more. But your only going to get good ID or even pick up smaller objects at usually 8", and depending on the objects conductivity, how it lays, ground conditions, etc, maybe only 6" or as much as 12".
Most good hunters sensitize their fields to just below where EMI effects it. Some push it for that extra inch or so by attempting to ignore a little EMI chatter. This takes a really good and experienced ear in my opinion. I love detecting as a "hobby" and not a competition, and am tickled at what I find at the 8" level.
Also, you will usually get better depth and not miss much if you do not notch. I believe it's better to ID the junk (pulltabs) yourself rather than depending on the machine just not lighting them up. Make sure you move around the target as you swing side to side, as the signal may change. And it may NOT be a tab after all. Notching it, you would have just passed up on a possible good target.
