The peak height has been found, the valleys on the side of each peak progressing to the center (inward sid of the peak, coming from the CRD toward the center, thus the right hand side of the left part of the image, and the left hand valley side coming from the right CRD meeting in the center where the N term peak is.

This means that each trimer valley value is taken from the side directed toward the N term peak  As recorded for widths and peak heights, the valley height is measure in all the separate trimers (N=172)(N=4).