  The spectral shape of the hard X-ray continuum of Active Galactic Nuclei
(AGN) can be ascribed to inverse Compton scattering of optical/UV seed photons
from the accretion disc by a hot corona of electrons. This physical process
produces a polarization signal which is strongly sensitive to the geometry of
the scattering medium (i.e. the hot corona) and of the radiation field. MoCA
(Monte Carlo code for Comptonisation in Astrophysics) is a versatile code which
allows for different geometries and configurations to be tested for Compton
scattering in compact objects. A single photon approach is considered as well
as polarisation and Klein-Nishina effects. In this work, we selected four
different geometries for the scattering electrons cloud above the accretion
disc, namely an extended slab, an extended spheroid and two compact spheroids.
We discuss the first application of the MoCA model to reproduce the hard X-ray
primary continuum of the bare Seyfert 1 galaxy Ark 120, using different
geometries for the hot corona above the accretion disc. We report on the
spectral analysis of the simultaneous 2013 and 2014 XMM-Newton and NuSTAR
observations of the source. A general agreement is found between the best fit
values of the hot coronal parameters obtained with MoCA and the ones inferred
using other Comptonisation codes from the literature. The expected polarization
signal from the best fits with MoCA is then presented and discussed, in view of
the launch in 2021 of the Imaging X-ray Polarimetry Explorer (IXPE). We find
that none of the tested geometries for the hot corona (extended slab and
extended/compact spheroids) can be statistically preferred, based on
spectroscopy solely. In the future, an IXPE observation less than 1 Ms long
will clearly distinguish between an extended slab or a spherical hot corona.
