Analytical models, describing laser Doppler flowmetry and its derived applications, are based on fundamental assumptions of photon scattering angles. It is shown by means of Monte Carlo simulations that, even in the case these assumptions are correct, the presence of a specific source-detector configuration may bias the shape of the probability density functions describing scattering angle behavior. It is found that these biased shapes are generated by selective filtering of photons induced by a particular source-detector configuration. In some specific cases, this phenomenon might invalidate laser Doppler analytical models.