Optical feedback interferometry (OFI) applied to microscale flow sensing is studied theoretically and experimentally. A new model is investigated that predicts the OFI signal. This model is based on the Lang-Kobayashi equations and highlights the importance of the laser beam propagation and the laser-particle scattering performances. For the first time, the angle distribution of the scattered light is involved in the model. The model evaluates the impact on the OFI signal of the light propagation in the micro-scale channel geometry. The flow rate measurement shows good agreement with the model.