Ratio of intensity from the Monte Carlo simulated HMXBs (left column) and LMXBs (right column) scattered along the Galactic plane (b = 0) by H2 (top row) and He (bottom row) to the intensity that would be scattered if all electrons were unbound. The range of scattering angles over which the Rayleigh scattering dominates the scattering cross section depends on the characteristic size of the electron distribution in the atom or molecule, which differs for different elements and molecules (see Sect. 4.1). This leads to a nonlinear dependence of the ratio of cross sections for different elements and molecules on the scattering angle. At each longitude many different scattering angles contribute, corresponding to the relative position of the X-ray sources w.r.t. the gas along the line of sight, resulting in the apparent longitudinal dependence of the ratio profiles.