If I am using one tone, I use the discrimination at a level to just break up unwanted targets, and listen for the clean signals. I started on a Tesoro so am still an audio hunter. The VDI works nice in parks, but at my iron laden sites tones are the only way to go.
Lower discrimination I use 2 tones or 3 tones, and listen for the higher tones. Basically it is a scale for me, the more discrimination the less tones I use. This seems to maintain the machines seperation and depth.
I rarely use high sensitivity unless going for deep signals. Most spots are too trashy and the machine starts falsing off every tiny bit of junk. I use just enough sensitivity to maintain decent stability in both air and ground conditions. In heavy iron I will drop in the 40s, old parks 80s.
Small coil, small coil, small coil. I rarely can even use my 11" coil, there is too much trash in my parks and especially my old sites. I have a NEL 5.5x9.5 that works much better as a general hunting coil, but the 5" coil is the best. I find more with that little coil than any other. It reduces falsing, runs more stable, less EMI and seperation is great. I wish the larger coils worked for me, but it is about worthless for my hunt locations. Great depth when I can work it, 11"+ coins in damp soil. When I go to the 11" coil, the Lesche Sampson comes out!
Old sites with carpets of nails I run Sen 40-60, Discrim 24-28 (depending on nail falsing/moisture), tones 1, 1+ or 2+ depending on mood.
Parks I run sen 70-85, Discrim 24-50 depending on trash targets, tones 2+ or 3. After ear fatigue sets in discrim goes up, and tone goes to 1, 1+ or 2+. Changing tones changes the monotany for me, and refreshes the hunt sometimes. I have not used the 3b much, but admit I hate bottle caps, but 3b seems to slow the machine down on heavy trash and can loose some deeper iffy targets.
The T2 is a great machine. I prefer my Tesoros in really bad iron, but the T2 holds its own and is much deeper with TID. A small tip, but this goes with any detector. A slightly positive ground balance is much more stable in the iron.