Another Day At The Park.

I wouldn't worry too much about similar tones, looks like your doing ok. Sometimes different density of a coin can give a different tone (depending on machine). For example a cold metal that has been struck using a die and hammer will be a lot denser than a modern cast piece of trash coin.
Just keep swinging and enjoy, looking at your hunts overall you doing an excellent job and remember every find is a goal - copper brass ally silver or gold.

I think it's about conductivity - silver and copper are the most conductive, and gold and zinc don't conduct particularly well (certain contacts are plated with gold not for conductivity, but because gold is inert and the contact will not tarnish). I don't think this is the whole story, though - my detector only has SILVER/COPPER, MID-RANGE, and IRON. Silver/copper is either actual silver (so far I've found one piece of 925 jewelry) or the ubiquitous pre-1996 penny. Mid-range is either trash or nickel coinage (1968-1999/2000/2012). Iron is almost always trash, OR MPPS coinage (so a new toonie gives the same signal as a rusty nail - oh joy!).