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We present a comparative study on an experimental and theoretical optimization of magneto-optical Kerr setups based on photoelastic modulation and phase sensitive detector methodology. The first and second harmonics, Iomega,2omega, of the reflected light intensity are measured for a CoO/Co magnetic reference film. The magnetic field dependence of the optical off-diagonal Fresnel reflection coefficients rps and rsp follows the sample magnetization. Different Kerr setups provide various dependencies of Iomega,2omega on the reflection coefficients and, hence, on the Kerr ellipticity epsilonK and rotation thetaK. Jones matrix formalism has been used to analyze the impact of a systematic variation of relative analyzer and polarizer orientations with respect to each other and with respect to the retardation axis of the modulator involved in longitudinal Kerr setups for incoming s-polarized light. We find one particular setup which maximizes Iomega as well as I2omega and maximizes the signal-to-noise ratio. Inefficient setups are characterized by Iomega,2omega intensities involving large nonmagnetic contributions of rp and rs.