The mirror tunnel is a component used to extend the depth of focus for compact imaging probes used in endoscopic optical coherence tomography (OCT). A fast and accurate method for mirror tunnel probe simulation, characterization, and optimization is needed, with the aim of reconciling wave- and ray-optics simulation methods and providing a thorough description of the physical operating principle of the mirror tunnel. BeamLab software, employing the beam propagation method, was used to explore the parameter space and quantify lateral resolution and depth of focus extension. The lateral resolution performance was found to depend heavily on the metric chosen, implying that care should be taken in the interpretation of optimization and simulation results. Interpreting the mirror tunnel exit face as an extended object gives an understanding of the probe operation, decoupling it from the focusing optics and potentially helping to reduce the parameter space for future optimization.