Well I run my Sunray 12" at 12 sensitivity on the beach. Now on my beach, that's as quiet as the stock 1050 coil. It will take higher sensitivity, but I find higher than that and I start getting the kind of falsing I need to keep checking and, more importantly,I don't see much of a depth gain. Seems VERY important to noise cancel PRIOR to adjusting the sensitivity. When I first started using a Quattro I used to noise cancel AFTER I had made whatever adjustments I made and that was WRONG.
Also, if you find after noise cancelling your Quattro is erratic (lots of falses) do it again. You probably noise cancelled over a very small, or very deep piece of metal.
Now you may find you can use higher sensitivity than that, depends really on your beach or beaches, they're all different I've found. Two beaches I use are about ten mile apart and one I can use higher sensitivity settings on.
I personally would recommend bumping the sensitivity up by one at a time, until you start getting false signals that are not OBVIOUS falses.
Even the Quattro's a bit of a challenge for new users, but after a few hours, all the things you learn, become second nature and you just instinctively do them without thinking.