1. With a wide open screen,I run gain at 30,This makes all signals loud,whether they are deep or shallow.
It wont make a difference on the shallow stuff,but it wasn't meant to,it will make any deep targets sound louder (Better).
If it is 20 or so you might miss deep targets,this is why to run it at 30.
Also with gain maxed out,there is no need to run fast on or deep on.
2.Over here,( I live in Missouri),I run sensitivity in manual almost always,The higher you run the deeper you can go.
I usually run 28,But i am not on your soil. The point is,To run sensitivity as high as you can also.
If it gets unstable (Chatters a lot even when not moving the coil), Lower the sensitivity till it is stable.
3. One other small note,I have noticed that with trash density high on, you may miss small targets if you are swinging really slow.
But you will want trash density high off in ferrous wide open anyway because trash density high was meant to be used with
some discrimination for it to work properly.
This should get you going.
Best of luck
LabradorBob