  This paper forms the second part of our study on how the neglect of NLTE
conditions in the formation of Fe I 6301.5 A and the 6302.5 A lines influences
the atmosphere obtained by inverting their profiles in LTE. The main cause of
NLTE effects is the line opacity deficit due to the excess ionization of the Fe
I atoms by the UV photons in the Sun. In the first paper, the above
photospheric lines were assumed to have formed in 1DNLTE and the effects of
horizontal radiation transfer (RT) were neglected. In the present paper, the
iron lines are computed in 3DNLTE. We investigate the influence of horizontal
RT on the inverted atmosphere and how it can enhance or reduce the errors due
to the neglect of 1DNLTE effects. The iron lines are computed in LTE, 1DNLTE
and 3DNLTE. They all are inverted using an LTE inversion code. The atmosphere
from the inversion of LTE profiles is taken as the reference model. The test
atmospheres from the inversion of 1DNLTE and 3DNLTE profiles are compared with
it. The differences between models are analysed and correspondingly attributed
to NLTE and 3D effects. The effects of horizontal RT are evident in regions
surrounded by strong horizontal gradients in temperature. In some regions, the
3D effects enhance the 1DNLTE effects while in some, they weaken. The errors
due to neglecting the 3D effects are less than 5% in temperature while the
errors are mostly less than 20% in both velocity and magnetic field strength.
These errors are found to survive spatial and spectral degradation. The neglect
of horizontal RT is found to introduce errors in the derived atmosphere. How
large the errors are depends on how strong the local horizontal gradients are
in temperature. Compared to the 1DNLTE effect, the 3D effects are more
localised to specific regions in the atmosphere and overall less dominant.
