Hey Bryce, here's nickel CZ experiences of note:
Sidewalk work, clay base, '83 shield at 6" on edge in thick clay Read round tab with my CZ-20 8" coil. Turned the disc up a notch and it became a very infrequent foil or square tab signal.
Buff in the river, under 8" of goose muck and soft sediments but it still had great finish on it most likely from lack of oxygen. Read clear, solid nickel on my CZ-7 with the 10" coil.
'23 Buff at 8" in trashy park with same machine, 8" coil again clear nickel signal and a highly detailed coin.
Too many buffs to count with my CZ5 but almost all read foil consistently. All the shields and V's I've dug have been clear nickel signals with the exception of a few slanted or on edge for all the CZ's. Been lucky to find those places in the park where the others ignored that target range in the past.
War nickels are all clear nickel reads in my experience also with all three CZ models I've had/have.
Since I hit a lot of sidewalk/parkway construction sites it seems their signal gets dumbed down by the matrix. So you gotta dig the low tones in those areas.
So in that park ground, look for those foil signals that pinpoint sizing and depth closely resemble coin-sized targets and you can't go wrong. Whichever one of your CZ's get you the best info with that method is the one to use. I believe my CZ5's with the 8" coils have been best at that.