You can't cover it all. I have written several articles to that effect. No matter how much ground you think you are covering up top, down at peak depth your coil signal is covering an area about the size of a quarter. With that in mind one can well visualize how much real estate you are actually missing at depth. Since most coins or rings will fit into a one-inch square and say you are hunting a 10" x 10" area - that area will contain 14,400 square inches or 14,400 potential targets. Now you can see why you can't get it all unless you dig up every square inch in that plot and sift it. The logistics of coinshooting can become mind boggling when you get down to the real facts. The average football or soccer field could contain nearly 500,000 - 600,000 potential targets. How many times would one have to hunt that field to cover every one of those inches? So when someone tells me an area is all hunted out, I just say " phooey."
Even if you overlap each swing 50% you are still missing a ton of real estate at depth. To even come close to covering everything at depth one would have to move their coil ahead one inch at a time each swing and scan in a straight line rather than an arc. One way to find more targets takes a world of patience but works. Stand still and scan every bit of ground in front of you several times, out as far as you can reach in front of you, remembering that one inch of coverage at depth, then stop your coil on the last pass and leave it sit where you stopped it, then walk up to your coil, stop and stand still, and repeat the procedure. If you have the patience try it sometime. You may be surprised at what you find, but don't expect to find a pile of coins every procedure because coins don't drop like rain.
Bill