  We have measured magneto-optical signals obtained by exciting the $D_1$ line
of cesium atoms confined to an extremely thin cell (ETC), whose walls are
separated by less than one micrometer, and developed an improved theoretical
model to describe these signals with experimental precision. The theoretical
model was based on the optical Bloch equations and included all neighboring
hyperfine transitions, the mixing of the magnetic sublevels in an external
magnetic field, and the Doppler effect, as in previous studies. However, in
order to model the extreme conditions in the ETC more realistically, the model
was extended to include a unified treatment of transit relaxation and wall
collisions with relaxation rates that were obtained directly from the thermal
velocities of the atoms and the length scales involved. Furthermore, the
interaction of the atoms with different regions of the laser beam were modeled
separately to account for the varying laser beam intensity over the beam
profile as well as saturation effects that become important near the center of
the beam at the relatively high laser intensities used during the experiments
in order to obtain measurable signals. The model described the experimentally
measured signals for laser intensities for magnetic fields up to 55~G and laser
intensities up to 1~W/cm$^2$ with excellent agreement.
