The Tesoro Toltec II uses the ED-120 discrimination circuitry similar to the Silver Sabre II, Bandido series, Golden Sabre II, Pantera, and most models made since those entries.
The earlier Tesoro's, such as the Inca, Silver Sabre and Silver Sabre Plus, 'original' Eldorado (replaced by the Bandido), Royal Sabre, Golden Sabre and Golden Sabre Plus, etc., had the more limted discrimination adjustment range on the lower-end. At minimum they still,had a LOT of rejection adjusted.
When Teosro improved their line and went with the ED-120 (Expanded Discrimination) circuitry, they definitely reduced the amount of target masking in iron infested sites.
Just remember, however, that while you might not suffer from some target masking with the audio circuit, the TID might still lock-on with an iron reading or be jumpy, or lock with a lesser TID reading that what a good-target ought to be, all because of a nearby masking target.
Now, you said the discrimination now reached well down into the iron range, and it most certainly does NOT do that! The former low-setting in Discrimination was well above iron nail rejection and also knocked out some small foils and small gold chains and cut into performance on the smaller, thinner gold rings.
The ED-120 discrimination accepts targets down lower in the conductive range, but doesn't get into most common iron. At the minimum Disc. setting you are at a point just a little above iron nail rejection.
Models such as the Eldorado, Vaquero, Tej