Thank you for your reply. I am still struggling to understand why SAR distribution is disruptive for IEEE 62704-4 Algorithm, whereas for gridless, it is smooth. Even in CST software, it is smoother. 

I have reviewed all HFSS, helping material, and IEEE standard for FEM. But, still not understanding it. I have increased the mesh of the model by assigning it inside the tissues --> select humanaverage tissue --> assign mesh --> inside --> length based -> max element 10000. It is still the same.