The phenomena of phase compensation instability (PCI) and mini-shear, i.e., the nonuniformity of the turbulent wind velocity along the propagation path, are discussed. A model is developed that describes the sections of the atmosphere in a way that allowed for the mini-shear induced fading-away of old heating patterns, previously deposited in a section. It is found that, for rather high laser power-density and high spatial frequency perturbations, there was a very pronounced and quite early onset of exponential growth of the Green's function solution, i.e., an early and clear manifestation of PCI. For lower spatial frequency perturbations and/or lower laser power densities, the long term behavior was virtually constant, i.e., there was no PCI. It is concluded that PCI could occur only if the laser-power density were high enough and if the adaptive optics could correct for high enough spatial frequencies.