Theoretical relation between the ratio of R = C₂₈₀₀/C_L, (left side of y axis) and formation height of CBs above the photosphere computed using the grid of 243 models (Berlicki & Heinzel 2014; Grubecka Litwicka et al. 2016). Each color represents a different formation temperature from 1100 K (orange, the lowest dots) to 5500 K (pink, the highest dots), with a step of 550 K. Two vertical lines indicate approximately the boundary heights of the formation for three different types of the CBs studied in Grubecka Litwicka et al. (2016). Type 1 CBs form on the left of the red line, Type 2 CBs between the green and red lines, and Type 3 CBs on the right side of the green line. In addition, temperature profile (right side y axis) from VAL C model atmosphere (Vernazza et al. 1981) is overplotted with a solid black line.