From your post you are already starting to figure it out. Size and the detectors ability to sound off on the object are two big clues.
If the digging is easy and the grass is healthy I still dig a lot of them up. Get rid of them, recycle and make the money from the aluminum and then check where they were. These big targets cover up a lot of good little targets under them and close to them.
Tough digging means you just move on. You will find that these huge signals will show up and you will start to use them almost like a road map of your hunting areas. One of the best stories was a group of guys who always hunted an old church yard. They all hit this piece of pipe and they all learned to ignore it. They even talked about it among themselves and then one day a guy decided to dig the pipe to see if it was masking anything. The pipe turned out to be a full roll of silver quarters that had been dropped and spread out
in a straight line in the grass. Time buried them and they became "a piece of pipe". These are some of the things that make it challenging
Don't give up on your CZ, it is one of the best.
HH, Don