  The accretion flow within the magnetospheric radius of bright X-ray pulsars
can form an optically thick envelope, concealing the central neutron star from
the distant observer. Most photons are emitted at the surface of a neutron star
and leave the system after multiple reflections by the accretion material
covering the magnetosphere. Reflections cause momentum to be transferred
between photons and the accretion flow, which contributes to the radiative
force and should thus influence the dynamics of accretion. We employ Monte
Carlo simulations and estimate the acceleration along magnetic field lines due
to the radiative force as well as the radiation pressure across magnetic field
lines. We demonstrate that the radiative acceleration can exceed gravitational
acceleration along the field lines, and similarly, radiation pressure can
exceed magnetic field pressure. Multiple reflections of X-ray photons back into
the envelope tend to amplify both radiative force along the field lines and
radiative pressure. We analyze the average photon escape time from the
magnetosphere of a star and show that its absolute value is weakly dependent on
the magnetic field strength of a star and roughly linearly dependent on the
mass accretion rate being $\sim 0.1\,{\rm s}$ at $\dot{M}\sim 10^{20}\,{\rm
g\,s^{-1}}$. At high mass accretion rates, the escape time can be longer than
free-fall time from the inner disc radius.
