Hi Marc,
The audio and ID systems on the T2 are independant and the info is ggathered differently. It's detailed in the manual and maybe mentioned in a thread here somewhere.
I can relay the results of a few air tests, and others with more experience and greater hours on the machine can chime in with their impressions.
I'm finding my machine chatters a bit at zero disc, call it a threshold noise if you will, but targets come in easily over this with stronger audio.
I tested a clad and silver dime at zero, 10 (default) and 80 (max) disc. I also tried a new, dime-sized steel washer, both alone and with the silver dime.
Tones 1, sensitivity default 60. Higher sensitivity numbers will increase the depth, but indoors, it was unstable for me above 60.
At 0 and 10 disc, the clad dime read to 6 inches, the silver to 7. The threshold tone at zero disc seemed to add its volume to the tone's, so audio was a tiny bit stronger with no disc at all. At 10 disc, the audio was quiet till the coin was swept by, same maximum distance.
By 80 disc, depth seemed the same or nearly so, but the audio was weaker. I know from other air tests that ID will become erratic before the audio fades away. I didn't pay much attention to ID in today's tests, but when I did check, it read correctly. Much further than this distance, ID became erratic, but still read in the coin range.
The washer was already being disc'ed out at 10, but was clear at zero. Maximum depth of the washer was 6 inches. I didn't check in-between settings, but at 80 disc, it made no ID or audio, but I did notice that placing it right against the coil produced the siren alert and "Overload-Raise Coil" message. Which seems to say it is being detected at all times, just "knocked out" by the circuitry.
Placing dime and washer together at low disc added the strengths of the targets so it made a stronger audio and ID jumped around 14-27. Putting disc at 80, the dime alone read, with proper coin ID, and to about the same distance as the dime alone, 7 inches. At maximum distance, it began to depend a bit on the orientation of dime and washer. For these tests, I held them so they were almost touching.
When sensitivity is set to maximum and using all metal or pinpoint no-motion mode, I got an air test of a dime to 11 inches. Of course, disc is not used in these modes, but it gives you an idea of the machine's sensitivity.
Hope this helps!
-Ed