•Detailed numerical analysis of a magnonic reservoir computer based on a spin-wave active ring resonator is carried out.•We determined how physical parameters of the reservoir computer affect computational performance.•We demonstrate a potential for a significant increase in the reservoir computer efficiency. We carry out numerical simulation of the performance of a physical reservoir computer based on a magnonic active ring oscillator. Our numerical model is based on the theory of nonlinear spin-wave transient processes in magnetic films. We employ-two metrics to evaluate the performance, namely the short-term memory and parity-check capacities. Obtained results demonstrate that there exists high potential for improvement of performance characteristics of the reservoir computer. Finally, we formulate optimal physical parameters for the magnonic reservoir. Our numerical model shows that the optimized reservoir will be able to increase its short-term memory and parity check capacities by two times with respect to the experimentally demonstrated in recent papers.