bullshrink, glad you are doing a bunch of air tests, with a variety of coins and household objects. Play with swing speeds (speeds with which you wave your hand) too.
But as for the in-field actual outdoor hunting trials, you should try to hook up with someone proficient in your area. Is there a club? someone from an on-line forum to buddy up with? Even if it's just a place prolific in clad (just for experience sakes in the short run), because the MXT should be quite able to effortlessly pick up clad, and should reliably disc. out foil, for instance, if you so desired, etc...
When you buddy up with them, have them flag targets, both good and bad. Ie.: "I'd pass this one" or "I'd chase this one", and so forth. In this way, you can actually hear what they're listening for (albeit with your own machine's audio). Because there is simply no way in printed text, on a forum like this, to describes "sounds" in printed text. And no way for us to know exactly what you're doing, etc..
For example: when I first got an Explorer, I had the same type complaints as you are now saying. I hated it, and wished I'd got something else. But seeing that my buddies were finding stuff with theirs, deeper than my whites, I stuck to it, and painstakingly went out to places where my whites used to get silver and wheaties (certain there must be more deeper stuff there). But time after time it just made no sense, quacked all over like a flock of sick geese, and didn't give accurate readings IMHO, and so forth. So these friends would try over email to describe to me how to swing, what I was supposed to be listening for, and so forth. To no avail. I was about to pitch it. Then one day, one of these guys who was an expert explorer user, took me to a particular park in his town where he'd been getting silver. We took turns flagging targets, going over the pro's and con's. I watched how he swang, what he was trying to isolate, etc... Likewise anytime he passed a signal, I'd press him for "why?". In 20 minutes the LIGHTS WENT ON, and I've been hooked ever since. See? No amount of printed text could do what an actual in-field trial with a user who can flag signals, can do.
Preferably someone with a MXT. But if need be, just someone who is proficient with whatever they use. And don't try to be a hero going to a heavily hammered place for this: pick a spot that is just prolific in targets, even if they're clad. And also not too junky either. The progress to slightly older yards from the 1940s/50s, for instance. And so forth.