For the optimal angles between 153° to 123°, we obtain Aiso values ranging from 37.56 to 26.15 MHz. Such values are approaching the experimental upper bound of Aexp= 20.6 ± 1.1 MHz for 61 NiPACN-0.5 wt% samples. Further distortion from square-planar to almost fully tetrahedral geometry (92.5° dihedral angle) yields a low Aiso value of 9.19 MHz.