Richard one thing I've learned to do on shallow finds is to simply lift the coil off the ground a few inches. If the signal comes in loud and clear after that, then you know it's a shallow find. If it stays real strong, it's a large target and almost always for me a soda can or piece of one. I only use the smartfind screen which is pretty good at giving you a good 'look' at what the coil is over. I'm no expert by a long shot, but I've done OK with it so far and getting better all the time. Just wish I had a little more time to devote to the hobby!
GL HH