The complex relationship between the mechanical stimuli arising in the context of haptic interactions and the perceived tactile properties, such as softness, remains underexplored. Mechanoreceptors placed in the human skin activate in response to local mechanical straining of the skin itself, resulting in what we understand as tactile perception. According to the Tactile Flow paradigm, it is possible to understand haptic softness discrimination in humans by measuring the growth rate of the contact surfaces on the skin. To validate this approach, we estimated via Finite Element simulation the mechanical strains arising in the fingertip skin during contact with objects of varying softness. We show that the Tactile Flow model also holds true when applied to the evolution of the iso-strain curves in the touch-sensitive layers of the skin, substantiating its relation with how humans perceive softness.