Sounds plausible. I have the same opinion having cherry picked sites for high conductors and then go back over them looking for nickels. Another thing is the nickel is right close to the pulltab range as well as other types of trash, foil, shredded foil, etc. Nickels generally over time have corrosion along with their being low in conductivity make for a harder time to find as well. I have found that I have to be willing to dig more trash ratio than for other coins so in part it causes me to look for them lastly compared to the clad coins but don't forget them in your hunts, from foil up to the nickel is a good area to find gold rings. For the ones using conduct sounds, if you place a dug nickel in one of your shoes, you can compare the tone to a signal in the ground, that way you can go for an exact tone match and maybe not dig as many pulltabs. I have found most nickels measure at 5 on the conduct scale and 6 is in the area of some pulltabs so that will give an idea of how I go about hunting them but the exact tone is mainly what I go by and yes I am sure using that method I will leave some nickels in the ground.