Normalised total diurnal sublimation energy, integrated over one diurnal period, displayed as a function of the fracture wall angle and analysed for four illumination scenarios. The sublimation energy is normalised to the total irradiated energy in all areas of the fracture. The circles denote calculated values, the lines show the trend employing cubic interpolation functions. All calculations were performed for 2.0 AU heliocentric distance and surface ice at the fracture floor only. The grey line indicates the total sublimation energy for a flat surface, if we assume that parts of the surface are inert: the sublimating area of the flat terrain equals the ratio between bottom and top width w_b/w_t.