I bought 2 different Sovereigns that someone done this too and they complained that they were not getting the depth some were saying and were putting their Sovereigns for sale. I bought them and seen right away the tones were set too high and was very hard to tell the difference in the close tones as nickle even sounded like a copper coin does without the tones turned up all the way. I did a few test and seen for me the depth increased when I set the tone like it came from the factory. Maybe it is my hearing, but do know I got plenty of depth out of each of these Sovereigns.
Now on the deep targets once you know the Sovereign the tones will be climbing and you can tell it is a very deep one, the tone will climb and not lock on to one tone as you do the Sovereign wiggle and most of these are just a slight threshold change and why the threshold is so important to begin with. These when doing the wiggle like I say you will hear them repeat and the tones trying to climb. On the new GT I have notice they will climb to the correct tones and ID on the deep ones and why I feel the new GT is more sensitive.
When it comes to the Electronics of a detector I feel the designer of the detector know more than I do and has the equipment to set it to the correct spec, so I learned not to mess with them other than try to put them back the way they were on those some feel they know more than the engineers do.
Rick