Spectra observed towards the center of IK Tau and χ Cyg (solid lines) and obtained by spatially integrating over the emission regions (dashed lines). The latter are shown scaled for comparison. The widths at zero-power of the J = 2−1 and J = 1−0 lines appear to be similar for IK Tau. Self-absorption is well detected in the CSEs of both stars, i.e., blueshifted J = 2−1 emission from warm gas in the inner CSE regions is partly absorbed in the outer layers. In χ Cyg small wings are detected at zero-power in the J = 2−1 line.