Why are Matsya, and Kurma incarnations of Lord Vishnu portrayed similar to Narasimha avatar? Even though they cannot be classified as half human being and half animal? Or did Perumal appear as half human being and half animal during these incarnations?

Matsya, Kurma, and Varaha incarnations are wholly in their forms (as fish, tortoise, and boar respectively); Perumal’s divine form is projected on these to highlight that these incarnations of Perumal; and these, unlike the incarnation of Narasimha which was half human being and half animal.