Re: Permeability
Actually µ isn't affected at all by the dimensions of the ferrite material you're using. But it is affected by the amount of magnetic flux passing through. This is what we call the hysteresis effect.
Concerning you're question, I assure you once again that µ isn't changed among the 2 shapes you showed. It is a constant characteristic of the material itself. While The reluctance (magnetic resistance of material) is affected
reluctance = L/µA, where L≡ length of substrate, A≡cross sectional area, µ≡permeability.