It's a 6 inch coil. It's not going to slam on deep coins, and coins at the edge of detection can sound like iron. That's not unique to the Nox 6" coil.
I have a permission where all of the older coins are 4"+ and many of them pinpointer deep or more. I can dig a dozen coins with the shovel and not one of them under 5 inches. After I got the 6" coil I took it out there and ran it wide open and was digging those coins. Plenty of them. Then, I took it to an area on the same permission that is a 40'x 100' blanket of pure pull tabs at 3 inches. I've pulled very few coins out of that area with two different detectors, including the 5x8" coil on the AT Pro but i know they're there. I cranked up the recovery speed, turned down the sensitivity, and the 6" coil was hitting on newer coins tucked between those pull tabs.
I've taken it back to two residential permissions and re-hunted trashy high traffic areas that have produced coins and buttons in the past. Off the top of my head, the 6" Nox coil sniffed out a thin aluminum early 1900s cafeteria token, a small US Amy medical lapel pin, and a civil war cuff button. Again, these were all areas I've gone over many times. Would I have found those items if I had just spent even more time with the other detectors/coils? Maybe. Maybe not.