  We study the extent to which Milne-Eddington inversions are able to retrieve
and characterize the magnetic landscape of the solar poles from observations by
the spectropolarimeter onboard Hinode. In particular, we evaluate whether a
variable magnetic filling factor is an adequate modeling technique for
retrieving the intrinsic magnetic properties from every pixel in the polar
field of view. We first generate synthetic spectra emerging from a numerical
simulation of a "plage" region at an inclined line of sight of 65$^{\circ}$,
and degrade the data to emulate real observations. Then, we invert the
synthetic spectra with two Milne-Eddington inversion codes that feature
different treatments of the magnetic filling factor, and relate the retrieved
magnetic quantities back to their original values in the simulation cube. We
find that while the apparent retrieved magnetic properties map well the
spatially-degraded simulation, the intrinsic magnetic quantities bear little
relation to the magnetic field at the native resolution of the simulation. We
discuss the systematic biases caused by line-of-sight foreshortening, spatial
degradation, photon noise and modeling assumptions embedded in the inversion
algorithm.
