Magnetic shielding

Hello,

Can someone tell me if I make a magnetic shielding by selecting the boundary's and specify a thickness (ds) and permeability on some wires it would be the same as if I just created a shield in the geometries and specified the material, thickness and permeability?

I've tried to make magnetic shielding on the parallel wires model there is to find in the model library. When I give the shielding a thickness and permeability the shielding doesn't show any clear effect on the result when I measure the magnetic field, but if I make a "shield" around the wires using the geometries and give it the same thickness and permeability it is very effective. I don't really understand what I'm missing, maybe my physic isn't good enough, but hope you can help me! :)