When you say air test are you using a single item on the ground under your coil? If you are in disc mode 0 then you should not expect to hear more than one tone frequency, either low, mid or high depending on the target.
In disc mode zero, have a nail, a pulltab, a nickel, a zinc cent, a copper cent, a dime and a quarter laid out with seveal inches to a foot between them. Once you understand the different target categories for these objects it gets easier. You'll hear a low tone over the nail, mid tone over the pulltab, depending on it's make-up, and high tones over the coins. Now turn your disc up one notch at a time and see where you stop hearing each target until you get to the high coin category.
As for pinpoint mode, it is a variable frequency that increases as you come closer to being directly over the target. That means the sound gets higher-pitched until you are directly over the target. Learn pinpointing until you are blue in the face. Learn to determine where that target is under the coil when the PP gives the best indication, this is the single best thing to learn on your machine. Finding the target quicker gets you looking for the next one sooner. Put the target under some cardboard, Use the disc mode to determine roughly where the target is then go to PP and hone in on it. Mark the spot on the cardboard, then check to see if you're right, but always air test from 4-6 or more inches above your target. Learn to pinpoint from that height too and you'll be spending a lot less time digging and scooping.
Of course real world means keeping the coil close to the ground but for learning that new machine in the otherwise useless medium of air do everything from the greatest distance possible. This holds true for all machines.
Now, repeat all that in autotune and you'll be well on your way down the rabbit hole.
anyway you get the picture.