I have heard that the DFX has measures that the E-Trac does not have, AC, DC, and a graph of harmonics or something, that aid meaningfully in differentiating gold rings from junk. The V3i may have those as well. That may be why your friend found the ring so easy. I bet it rang up in the teens CO. This would allow one to cherry pick a park for gold, leaving pulltabs behind and some odd gold with them, but finding many easy targets.
You should have scanned the ring with your E-Trac after he found it. I guy I was hunting with found a class ring with his F2 big enough for a quarter to fit inside of it, and it rang up 12-36.
The real reason less gold is found with an E-Trac is that we get so spoiled with 80+% accuracy on quarters and dimes that we get tired of digging every pulltab and piece of canslaw!
A friend with an E-Trac accidently found a gold chain very thin and tiny links with a small cross while digging another target, and it would not register at all on his E-Trac. The friend with the F2 found a silver chain resembling a lamp pullchain, and it would only register a very low CO I forget what when rubbing it on my coil. Both were due to the small links, larger targets will atleast register, but you have to dig them and it is hard to do when you have a detector that is this good at differentiating coins.