The whole point of a counterpoise is that it doesn't need a physical connection to ground. If the radials are 1/4 wave then the current at the ends will go to zero but the Z at the central connection point will be low. a bit like a quarter wave VHF vertical with 1/4 wave earth rods. In practice a counterpoise near the ground will capacitively couple to it so it makes the whole thing a bit of a halfway house and for LW, very big. No real advantage over a good ground mat of similar dimensions but might be easier to construct ... possibly