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We perform a simple sensitivity analysis of a W1 waveguide bend in a photonic crystal (PhC) where we use the information obtained to optimize the PhC bend???s frequency response. Within a single optimization step we already achieve very low power reflection coefficients over almost the entire frequency range of the photonic bandgap (PBG), i.e., an achromatic bend. A further analysis shows that there is a single critical rod in the optimized bend structure that exhibits an extraordinary high sensitivity at a given frequency. Hence power reflection becomes tunable from 0 % up to 100 % involving only small changes in the critical rod???s properties. This opens the door to novel topologies for compact switches and sensor applications.