Growth of fractional Hα flux vs. the growth of the fractional covering area. The flux contributed and the area occupied are measured from the same minimum surface brightnesses as in Fig. 3 up to a given relative surface brightness. The values of these relative surface brightnesses (Σ/﹩\overline{\Sigma }﹩) are marked by ticks increasing from 0.4 (lower left‐hand corner) to 3 (upper right‐hand corner) with a step size representing a factor of 1.25 increase in surface brightness. The area is normalized in the same way as in Fig. 3. See the text for details.