Sensornet lifespan and utility is limited by the energy resources of individual motes. Network designers seek to maximise energy efficiency while maintaining acceptable Quality of Service. However; the interactions between multiple tunable protocol parameters and multiple performance metrics are generally complex and unknown, and combinatorial explosion renders impossible any exhaustive search approach. In this paper we describe an engineering method to address this multi-dimensional optimisation problem. We apply a Design Of Experiments approach to sample the entire search space. Statistical models are fitted to experimental results to define relationships between inputs and outputs, and to obtain near-optimal solutions.