Comparison of observed cyclotron line variability in GX 304-1 with our model. Panel a (b) shows the CRSF centroid energy (width). Red and black circles represent the observed E_CRSF and σ_CRSF values of GX 304-1, obtained using the CYCLABS model (Lorentzian profile) and the GABS model (Gaussian profile), respectively, to fit the line feature (Mushtukov et al. 2015b). Green, blue, and purple lines correspond to the results derived from our MC simulations for three different viewing angle intervals. The model predictions, for specific viewing angles, agree sufficiently well with the data over an order of magnitude in luminosity.