Sensitivity should be set outside, away from elecrical interfrerence. adjust it till it "chatters" then back off some. It will go deeper with higher levels of sens. but at the price of chattering and false signals. You need 'just' the right amount of sensitivity, not too little, and not too high. For me the inside controls, once I set them, I leave them set this way and never change them. I set my sensitivity once when I bought it, also set the threshold to a just audible setting, then air tested a quarter with headphones on and set my headphone volume to a pleasant level.Then I closed the case as this is the way I always run the Tiger Shark.
Ground Balance the Tiger on metal free ground, I use All-Metal (FAST) mode and bob the coil from about 8" from ground to about 1" above ground with a brisk raising and lowering of the coil. Pay no attension to the threshold sound on the uplift of the coil but do pay attension to the downstroke of the coil. If threshold gets louder as you lower the coil, turn ground balance knob counter clockwise a little, if the threshold goes silent on the way to ground, turn ground balance knob clockwise some. You need to have a ground balance setting where the tone stays the same hhhhhhhuuuuuuuuummmmmmm when raising and lowering the coil. This is called a neutral setting and works the best for me in my ground. Hope this helps.