Can slaw as we call it is hard to tell sometimes. One thing you can do to eliminate digging the big stuff is raise your coil 4-5 inches off the ground, if the signal is still solid and loud, it is probably a very big item. Just get to know the machine and you will be able to pick out the sounds. Believe it or not there are very subtle differences to the way different items sound. It's not just tone. Pitch, intensity, and other little things can help you out after many hours on the machine.
That being said, If you are avoiding all but good high tones, you are absolutely missing hundreds of good targets. I used the tracker 4 last year and I dug soo many iffy signals and ended up with some awesome stuff. The tracker 4 is not a high end machine, so you have to put the time in and DIG DIG DIG. after a couple 5 gallon buckets full of trash, you will have a very good handle on the machine and when you do, it will bring some great stuff.
Good luck.