We present an in-depth analysis of the angle and mode tuning dependence of the polarization splitting in detuned organic microcavities. The system consists of highly reflecting dielectric mirrors comprising a continuous wedge-shaped cavity layer of 4, 4′ -bis(N -carbazole)-biphenyl, doped with 2 wt % of 4, 4′ -bis[(N -carbazole)styryl]-biphenyl as the active material. By varying the measurement position across the sample, we shift the resonant mode with respect to the center of the cavity stop band. Starting from small detunings, the splitting value increases non-linearly up to 58 meV, when the resonant modes reach the stop band edge. We compare this behavior with results from transfer matrix calculations and theoretical predictions.