You got up-averaged on that nickel.
Fishers are designed to do that around iron and in mineralized soil, even a little bit of mineralization.
The deeper the target the higher the numbers can go.
What were your GB numbers and how many bars on your dirt meter at this site?
In Kansas and Missouri dirt average GB numbers were from the mid 40's to maybe the mid 50's a few places with one bar on the dirt meter...if that, most times I had no bars.
Not a lot of up averaging going on there from what I saw.
Where I live now in Alabama numbers are always in the low to mid 60's at least but frequently go into the high 60's, 70's and up to th low 80's and usually with full bars on the dirt meter.
In my difficult SE. red devil dirt, even the not so red black stuff, all my numbers soar as you get deeper...even past 2".
A regular nickel here is 32 on the surface, 40's -50's at 3-4", at 5" and definitely 6" or more it is into the high 80's to low 90's every time and all of them...buffs, V's, war and any other Jefferson's.
All my targets up-average here as they get deeper, IH's, clad, all coins and even trash and I use that knowledge to my advantage...once I learned a different numbering system for my deeper targets.
I found out recently in my dirt my Mojave up averages pretty good here too.
A few used this thread/log I started to cut down the learning curve a bit they tell me.
Everything I learned, observed and discovered for the first 7 months I used my F70 and all my settings and results in good Kansas soil.
http://metaldetectingforum.com/showthread.php?t=173474
I am an insanely mad and anal tweaker, I tried a ton of settings plus continued to do that after I stopped adding to this thread.
Here in the SE. it is a whole new and different ball game but I have written a lot about how I hunt here and my settings and observations in other posts.
Great unit, I have done more than well with mine in every site I have taken it to so far.
I have yet to come across a site or any conditions it could not conquer with the right settings