Parameter study showing the SED and Q-band FWHM as a function of the inner radius of the outer disk. From top to bottom: HD 97048, HD 169142, HD 135344 B and Oph IRS 48. Left: the SEDs of models with a different location of the inner edge of the outer disk. Right: the FWHM sizes of these four models as a function of the location of the outer disk wall, given for the Q-band at 18.8 μm (HD 169142 and Oph IRS 48) and 24.5 μm (HD 97048 and HD 135344 B). The horizontal dotted and dashed lines give the FWHM sizes of the observations and calibration stars (PSFs) respectively. The variation in the FWHM as a function of the position angle is given by the grey and light cyan boxes (observation and PSF) and the error bars of the models. The colors on the left and right figures correspond to similar models. The vertical dashed-dotted line shows the chosen parameter of our best-fit model. We note that for Oph IRS 48 the semi-major axis of the MIR image is fitted, but not the FWHM.