PDF of formation height as a function of transition region height (defined to be the lowest height in a column where the temperature is greater than 30 kK) for the C II 133.4 nm line (left) and the C II 133.5 nm line (right). Each column in the panels is scaled to maximum contrast to increase visibility. The green contours encompass 50% and 90% of all points. The Pearson correlation coefficient is given in the upper left corner, the red line denotes y = x.