So I use a 10.5" coil on my CZ-20. This way, I cover more area. I'm not really worried about depth, as most targets are fresh-drops here.
Pinpointing underwater is a true test of skill. I don't worry about "seeing" my pinpoint location. I got my sound and feel. I use a modified "X-Style" of pinpointing. I move the coil left-to-right over the target, SLOWLY, and narrow down the distance moved as I get a beep in my headphones. Once I'm getting a sound when I'm only moving an inch or less (this is where the drag in the water actually helps), I'll start moving my coil forwards-and-back, again narrowing the distance down as I get a sound. Once I have that axis done, I may give the target a left-right-forward-back movement, and if I get a sound without moving the coil very far (an inch or less), then I have the target "bracketed". I place my coil down on the bottom over the target. Then, I move my left foot towards the coil, until my toe touches the coil. I move the coil over to my right side, and place my scoop on top of my foot, with the tip of the bucket angled down into the sand. I start pushing it into the bottom with my hand, but remove my left foot and use that foot to drive my scoop into the bottom, in a down-and-forward motion, while at the same time pulling the handle back towards me. I then pull the scoop up to the surface to filter the bottom-material out and see if I got the target. This takes a bit of practice, as you can't see what you're doing.
HH from Allen in MI