Progress has recently been made in both the collection and modeling of fluid-optic disturbances imparted by compressible, shear flows. This field of research, termed Aero-Optics, has been motivated primarily by the development of directed-energy weapons; however, it is equally applicable to a general class of applications involving laser transmission and reception from aircraft. Examples of these-type applications include free-space, laser transmission from ground to air, from air to air and from air to space. In the present paper, we examine the effect of laser transmission through high-Mach-number, subsonic, compressible free shear layers on the ability to focus the beam on distant targets. Time-resolved time series of distorted wavefronts due to propagation through a Mach-0.8 free shear layer collected at the Aero-Optics facility at Arnold Engineering and Development Center, are used as the input to a Fourier-Optics routine that computes time series of far-field irradiance patterns. These patterns are then used to compute the time-averaged Strehl ratio directly, and these are compared to time-averaged Strehl ratios computed using the wavefront's rms Optical Path Differences and the large-aperture approximation. Conclusions are drawn about the appropriateness of using the large-aperture approximation for Aero-Optic-type wavefront aberrations.