Turning the sensitivity up does not effect the ID. I usually run mine at 5 bars but will turn it up to 6 on occasions if it will allow me without falsing. I have found though ,,with the sens turned up,,, if there are several shallow targets, close together. It is more difficult to seperate them, but all you need to do is turn it(sensitivity) down for a minute in order to dig these targets.
If the ground is dry(you didn't say) it causes problems for depth with any detector. But in general, if you are not getting any deep signals,,, its because there is nothing there.(even at 4 bars) Keep swinging they will come.
BTW I'm a coin hunter,the jewelry is a bonus for me. I set the ace in custom mode and everything below nickel is disc-ed out. Sens at 5-6 bars. Look for weak signals that read deep, they may not give a signal from certain directions and from others they are bouncing around,but yet somewhat consistant in this manner.I dig them all,, but if you can get a dime reading from any one direction on these, its a definite "dig". I have found a bunch of wheats this way and a few mercs. Not sure if that made sense, but tring to say ,dime ,penny size coins don't always read well at 5-10 inches. Another thing to look for when doing this , if reading 4-6+ inches on depth and then go into pinpoint and depth reading stays about the same, and is a weaker hmmm(not screaming and kind of hard to place) makes that target a more desirable coin size object.
Good Luck