The electrons pass through all part of the loop will be timely-correlated with the HXR assumed to be injection function. Qualitatively that’s it. However, for quantitative comparison the is one complication.  Now we assumed inhomogeity and so radiation at different field strength varies and for flux we need the cross section variation along the loop, with B in other words.  Therefore needed to consider magnetic field variation (three different cases) . Qualitatively The up-left panel-depening on where they are the radiation efficiency differs although same electrons. The bottom right, and also in some part it is optically thick and in some part optically thin. Thus a full expression is used. The right column show final model fit to the observation: different curves -> different magnetic field tube models how the tube cross section varies with B.