Tests of the fitting procedure with simulated data. Top: parameter search for data simulated with M_mid = 4 M_⊕, D_c = 10 km, R1 = 6.5 AU, R2 = 35 AU. Bottom: parameter search for data simulated with M_mid = 40 M_⊕, D_c = 350 km, and R1 and R2 as just mentioned. Levels are 99% (red), 90% (dark blue), 75% (light blue), 50% (green) and 10% (yellow). The two best-fit regions delineated by the 90% contour are clearly exclusive when comparing the two plots. Their peaks are close to the a priori values of M_mid and D_c. The two crossed circle symbols on each plot indicate the positions of the a priori values used for M_mid and D_c to simulate the two sets of data.