I have used all three detectors and have had no problems with the Sensitivity at 28 and audio gain at 8 to 10 in Semi-Auto in my area. However, I don't presume to tell anyone where they should set these functions as that depends on environmental variables and personal preferences.
Minelab has the presets at the middle of the adjustments. While audio gain has a dramatic affect on depth the sensitivity is more for signals with a small amplitude over the threshold level.
It would be interesting to know if you use semi-auto or manual as it is difficult to adjust the setting higher than you suggest in manual. However, in semi-auto there should be no problem unless there is a lot of external stray RF in the areas you detect.
I don't know about others but I make it clear that I am not suggesting that anyone use the setting I prefer as that is up to the individual.
However, you will find that I and several others also suggest lowering the sensitivity and audio gain depening on environmental variable such as external stray RF noise, ground minerals, co-located targets and what one is searching for. As an example I recently found a piece of jewlery that was lost in some grass. Since the item was had not yet had time to sink into the soil I had the audio gain at 2 and Manual Sensitivity at 5. I also used the learn mode to learn a duplicate of the item so searchined in discrimination. I found the item within 30 minutes.
<span style="background-color:#ffff00;">The best settings are the ones that works best for the individual in my opinion.</span>
Have a great day and how is hunting in your neck of the woods? What is the average depth of coins and relics and do you have problems with minerals? It would be great to hear form others in your state to see how they are doing.
HH, Cody