The best way to learn the machine and learn pinpointing with it, at least the FIRST thing I always recommend is this. Spend some time with a number of various targets like coins and jewelry of different types and maybe a trash target or two and lay them out on a blanket in a clean area outside. Put the sensitivity down to 16 and semi-auto for this, since the targets are on the surface...no sense complicating things. Now sweep the targets and see how that act. See how they pinpoint. Get a feel for the coil and the whole "Double D" thing. You should realize that what you have is two separate coils...opposing "D's", one on the left and one on the right. It's a little different than a concentric coil as far as how a target is swept and pinpointed but with a little practice you can get it. And when you master it, you can actually use that to advantage when in tight spots...having "two" coils.
One thing that can also help in situations like you're talking about is to raise the coil off the ground slightly while pinpointing. Unless the target is a large junk item, raising the coil slightly will make it "get smaller" (and easier to pinpoint) real quick. It's a technique I use often. And if you're thinking there are other trash targets nearby, try approaching the main target from another angle, with the edge of the coil...sneak up on it. Also, in trashy areas with multiple targets it can help to have a smaller coil, like the 8" or even a 5". And of course don't run the sensitivity too high because that can exaggerate those kinds of problems.