Answer:
The coefficient ζ for the consideration of the pressure force distribution in a flange is a correction factor to determine the critical buckling moment Mcr for certain boundary conditions and loads.
In RF‑/LTB, this correction factor ζ always refers to the largest bending moment of the equivalent member. The references in literature often give the coefficient ζ in relation to the center of the equivalent member (see also the RF‑/LTB manual).
However, RF‑/LTB also provides an option to define the zeta-coefficient manually. To do this, select the "Assign LC/CO Individually" option in the Method of Determining Mcr section (see the image).
