In this study, the validation of a stochastic model of broken clouds based on the Poisson point fluxes is considered. As a prototype of real cloud fields, realizations obtained by the fractionally integrated cascade model are used. To consider variations in the cloud optical thickness in the Poisson model, additional averaging of radiative characteristics in accordance with the probability density is proposed. The effective value of the aspect ratio, which is the most important input parameter of the Poisson model, is chosen from the condition that the mean nonscattered fluxes calculated with the Poisson and cascade models are consistent. It is shown that, for the conditions of low or moderate cloud fractions (N < 0.7) and of moderate light absorption by water droplets (the single scattering albedo > 0.95), this approach allows a more accurate calculation of the area-average diffuse-solar-radiation fluxes than the independent pixel approximation and than the model of horizontally homogeneous clouds.