Evolution of the ratio of the circularisation radius of the accreted wind matter from the O star to the radius of the innermost stable circular orbit of the BH for the 17 BH+O star binary models as a function of the time since the formation of the BH. Left panel: evolution as calculated by V20, which does not account for the orbital velocity of the companion and the typical wind velocity of O stars. Right panel: same evolution when we use the typical O star wind velocity (Eq. (1)), the mass of the BH, and the orbital velocity of the O star companion. The black horizontal line in both panels show the dividing line above which an accretion disk can form. The colour coding in the legend identifies the 17 progenitor WR+O star systems that are expected to give rise to the BH+O binaries.