We introduce a modified Monte Carlo model of light scattering in paper for better understanding of optical dot gain origin. Using a realistic description of paper as a scattering medium and assuming that light distribution in paper (generally any homogeneous or inhomogeneous substrate) depends on its optical properties, we tried to determine light distribution inside paper with known optical properties. In our description, absorption and scattering coefficients of all paper constituents were taken as key functions insofar as they contribute in a real printing application. Due to the fact that paper is a complex medium, it is necessary to involve, in calculations, its surface structure, which was modeled on the base of microfacets. Depicted phenomena were observed and calculated in transmission and reflection. Agreement of the statistical light scattering model in a complex substrate with experimental data demonstrates that the new method successfully describes the phenomena of interest.