No its not just Fishers! everyone has trouble with those tabs. The problem with the tabs is their supposed to be just a little higher than a nickel, but that's an average tab in perfect condition. If they get bent, they hit different, if its a little smaller they hit lower. The pull & toss tabs are the worse for me, the tab straight is good, bend it, its different, break the tab off and its lower, twist it up, clip it with a mower, and the report back is different. Tabs can dance around the nickel range and make it near impossible to sort them out in the ground from nickels. And its always been a problem sense they came to be in 1965 (pull & Toss) the sta-tabs came to be in 1975. I've had Whites, Teknetics, Fisher's, Tesoro's, Bounty Hunters, if your looking for in the ground nickels in an area where there is a lot of tabs then good luck! its not possible to sort out just the Nickels from the tabs. Now, if you've spent some time in the same area and watch the numbers for the nickels and the tabs real close then you can do better at sorting them out. At best for me in doing this is I have increased my nickel finds somewhat, but I'm still digging a LOT of tabs. (The sta-tabs are a little less of a problem)
Another problem I've found with Nickels and some detectors is after they get a few inches in the ground they start to go up the ID scale and fair amount, I've got a test garden (well seasoned now) and the 5" nickel with some of the Detectors I've had will ID at the Zinc penny range?
The six inch one goes a little higher. My Tejon seems to hold pretty close on the discrimination range at depth. With the ones I had that did this they would do the same thing air testing them, they would ID good out to about 4" or so, then start to clime from there until they just drop off. No! the other US coins don't do that, or I haven't found any that did.
Mark