Variation in coupling of unstable resonators is analyzed for the case of low order medium inhomogeneities. The analysis examines one-dimensional confocal unstable resonators with linear or quadratic index profiles in the resonator medium. These types of effects can arise from the bulk and wall heating present in gas lasers. The analysis shows that both the effective Fresnel number and the geometric magnification influence the local stability of the design point coupling. Choosing the Fresnel number to maximize mode loss separation may not be consistent with the choice of Fresnel number to minimize the influence of medium variations.