Sum of surface brightness profiles for some combinations of our inner and outer belt models, at 890 μm (solid lines). In each combination the inner belt is the same (e_max=0.1) and the outer belt has a different maximum eccentricity, as shown in the plot legend. Dotted lines only show the surface brightness of the outer belt models. The belts are modelled independently, and their peak surface brightness values are re-scaled to ring peak values from frank. The frank profile of HD 131835 is shown in red. For details, see Section 3.2.