see Manojlovic, J. Z. The Krafft Temperature of Surfactant Solutions.

Therm. Sci. 2012, 16, 631−640

Surfactants form micelles above the Krafft point and the solubility of surfactants in water increases drastically. Therefore, solubilization occurs above the Krafft point. The longer chain surfactants have low CMC's and are much more surface active (i.e. they are more efficient surfactants). Krafft points are affected by the nature of the bond between the surface active ion and  the degree of hydration.

The Krafft point of an ionic surfactant can be obtained by solubility measurements as a function of temperature. The concentration of dissolved surfactant in equilibrium with the residual crystalline surfactant increases dramatically beyond the Krafft point.