In Landau and Lifshitz volume 10 pg117 the authors say that the electric and magnetic fields $\vec E$ and $\vec B$ are averaged over regions "having dimensions large compared with the distances between the particles but small compared with the Debye length".
I have seen other authors say that the average is taken over length scales much larger then the Debye length.
Why would we want it small compared with the Debye length because surely this gives effects due to the fact that the fields have not being effectivly screened?
