Collisional and PR drag time-scales for particles in the planetesimal belt in our best-fit model outcomes. Two PR drag timescales are depicted: the time it takes for a (circular) particle orbit to decay from the belt to the star, and the time it takes for a (circular) particle orbit to decay from the centre of the belt to its inner edge. Scenarios A and B are shown in solid and dotted lines, respectively. Indicated at the top are the |$\beta$|-factors corresponding to the particle sizes for the material of Scn. A. |$\beta$|-factors for Scn. B are marginally larger, with a blow-out size shifted from 13 to 15 |$\mu {\rm m}$|⁠. Also indicated is the estimated stellar age of Fomalhaut of 440 |$\pm$|40 Myr (Mamajek 2012).