Each segment for a non-prismatic column could either have a linear variation or a parabolic variation. If the variation is parabolic, Substructure internally converts that to multiple linear segments for analysis and design purpose.

Column location is measured with respect to the left end of the cap. For each column you can specify bottom elevation. However, top of column is automatically extended to the centerline of the cap. In structural analysis as well as design, the length to the cap center line is used as the column length.