A restriction of kerrbb2 is that it is only applicable to those data firmly in the “thin-disk” limit (scale height ). The scale-height of the X-ray emitting region of the disk is determined by radiation pressure, itself set by the luminosity. Previous work has demonstrated that the presence of a geometrically-thin, optically-thick disk can be reliably assumed over the luminosity range , where the Eddington-luminosity (McClintock et al. 2013).