We must dig them aluminum. With my machine I can tell the pull tabs 99% of the time and the big cans 99% of the time, it's that last 1% that turns out to be gold.
I'm sure other places are different then what I see but Aluminum is lite and most of the time, it's shallow and I rarely dig it..but I do dig a few from time to time, just to confirm. Maybe one of the few targets I can guess correct.........xcal user only.
Shallow has two meanings for me.......one,... it's near the top of the surface, and shallow, in closer to shore.
It's about knowing the beach's you hunt, habits, target history and possibles.