typical tresures are 3-4 debth down when you use a pikaxe.
When it come to the snow biome then then you sometimes need to go deeper and look for it a bit harder to find the location of the silver below ground.
But yes its rather sensitive and can locating things from guess 50-100m away
So yes it could be you are in the max range and you only hear a single ping and then you know you have to run in another direction to find the tresure ( make it ping as fast as possible and then dig down ;-)