In a previous study, a two-dimensional non-stationary model of fire spread across a fuel bed, which included slope effects, was proposed. Improvements of the flame radiant contribution are made in the present paper by taking into consideration long-range preheating mechanisms. Fire front is assumed to be a radiant panel and the amount of energy impinging on the unburned fuel ahead of the fire front is estimated by means of a view factor. However, computation time of this view factor is lengthy and a simplified computation is thus proposed. The predictions generated by both models are compared to data recorded during laboratory-scale experimental fires conducted across pine needle beds for slopes ranging, from 0 to 30 degrees. First, the slope effects on predicted rates of spread, temperature distribution and fire front shapes are provided. The influence of fire front width on model predictions is also presented. This effect appears to be a significant variable affecting the rate of fire spread and is qualitatively represented by the model.