I have 4 different coil sizes and rarely use any of them other than the 8 inch stock coil.
What disc. are you using?
I usually set at 5 (Disc.1) and 7 (Disc.2) when searching a heavy trash area like you're searching and almost never get fooled on iron.
If I'm at a historic place that I want to dig iron, I set it at 2 (Disc.1) and 5 (Disc.2) and use the sensitivity pushed in.
I suggest my first example of settings so that you don't dig as much trash and get used to good sounding signals.
Disc. 5 will accept all non-ferrous (or 4 and a half) and 7 will knock out foil, pull tabs, some brass, etc. but will still find copper and silver.
Even though this machine is one tone, there are several variances of that tone and once you get used to it, you should always know an iron signal.
If you want to get another coil, I suggest a 5 or 3.5 inch one for heavy trash.
I find the 10.5 coil useless and tiresome. It doesn't really get anymore depth than the 8 inch.
Just like Tom's invitation....Please feel free to send me a P.M..
Cheers,
Dave.