Apparent radius (R _p ) of the peak temperature normalized by the gravitational radius (R _g ) as a function of days since the UV/optical peak. Only sources with no corona emission (see Section 4.3) are shown. The gray shaded region shows the 0.3 ≤ R _p /R _g ≤ 20 interval in which the measured R _p /R _g is statistically consistent with R _ISCO.