To dig large iron objects with FBS detectors is very easy at least with explorer ,but what I see etrac works the same. if you use open screen in ferrous you will never get high repetitive tone from small item in different angles, its only my experience and its only about old 1050 coil, because pro coil have only for short time -but its looks similar. so if you get high ,but a bit different sound -similar to copper but a bit different for not able to hear object borders and little bit similar to hot rock repetitive signal from different angle you can get large iron very deep. dont want to lie about how deep you can get but last my hunt found rusty plow 50x30cmsize and 3mm thick 60cm or a bit more deeper. I was using audio 1 and was not able to understand what was going because plow was under big stone. I dug and found stone? I checked with detector signal< i thought hot rock, cover it back with earth and was thinking to leave it, but decided to listen again and it was repetitive signal-have to add it was dark, I dug again and took stone off and got signal even deeper, it was big old Plow at least 100 years old and I suspect it was hided by original owner, because it was all in order and it was usual thing to do when people had to move from wars. but its my second plow treasure ,first was near friend farm house,we found where his grandfather in 1944 hided 4plows and bunch of horseshoe when Red army pushed back nazis from Lithuania and brought chaos and deportation to Saberia. No one in the family new about grandfathers secret. Good luck all in digging deep 
, Stasys
, Stasys