With deep objects, anything is possible for VDIs. But the objects I've found with high Fe numbers have been found in shallow (less than 3 inches) and deep (more than 6 inch) targets.
While I could use more time to learn my E-Trac, I'm already pretty accurate with it. Even after spending about 10 hours on it, I can tell if a target I'm about to dig is a coin or junk. And if it's a coin, I can usually tell if it's a penny, dime or quarter. I'm even more accurate with my E-Trac than my Equinox 600 (I've got closer to 50 hours on that).
The Equinox might ring up a target as a 22-28, but the E-Trac will ring it up as a 19:46 or something along those lines. When that happens, it's usually not a coin, but junk.
But the E-Trac has the unfair advantage of it's dual VDI ability. And before I dig with my E-Trac, I always go to all metal and check the Fe number. When it stays the same, it's more likely going to be a coin. But when the the Fe number goes up by more than a few points, it's almost always junk.
So no, I don't need more time on my E-Trac just to get my Fe numbers like yours. Oh, and all of the above observations has been made when swinging both the Equinox and E-Trac over the same unknown target, before digging.