Hello Aditya,
If I understand correctly, the nomenclature you are using is a little misleading. The sharp feature that you are referring to is a rising-edge feature and is not after the edge. The is a classic feature for square planar complexes and Ni does form a lot of those. The origin of this feature has been argued (in molecular systems) to be either:
1) Valence bond configuration interaction feature (VBCI), which is a formally forbidden 2 -electron transfer process. It gains intensity with covalent overlap of metal with ligands and has been shown (in the case of Cu(III) which is isoelectronic to Ni(II)) to increase with metal-ligand bond strength.
2) It has also been attributed to longer-range multiple scattering.
It is important to realize that both effect increase in square planar systems and usually such a feature is the hallmark of a square planar molecule.
Best,
Riti