Duplex components are one of the proposed concepts for actively cooled plasma-facing structures. This concept introduces a new source of stresses due to the mismatch in the coefficients of thermal expansion between the bonded materials. Normally and in order to ensure equilibrium singular edge stress fields are generated at the edge with high values of the involved gradients, and although confined to a very small region their characterisation is important because debonding starting from this region is one common cause of component failure. Castellated beryllium tiles brazed to a CuCrZr heat sink have been studied as prototype target plates for the pumped divertor phase of JET. For this system, an eigenvalue analysis is performed for the free-edge stress fields free of singularities and favourable local geometries are deduced. Based on these results guidelines for component optimisation respect to edge fields taking into account material properties and geometry are presented. In particular the strong effect of the local geometry is discussed.