Refer to FCOM Flight Crew Bulletin : FCB-FCB17 P 3/6.
"CHARACTERISTIC SPEEDS COMPUTATION A320
VLS is computed from Weight and Vc and corrected for the current CG. ‐ If the current CG is forward of 15 %, 15 % CG is used to compute the speeds ‐ If the current CG is between 15 % and 25 %, the speeds are computed using an interpolation between 15 % and 25 % CG ‐ If the current CG is aft of 25 %, 25 % CG is used for speed computation. F, S, and Green dot are independent of CG"