The concept of stirring coherence time has been recently introduced as an effective way of measuring the ability of a mechanical stirrer to introduce disorder in a reverberation chamber (RC) and predicting the stirrer efficiency under any loading condition. This paper builds upon those findings by introducing the intrinsic stirrer efficiency parameters (ISEP), which are independent of the RC features. Tests in three different RCs confirm the viability of this approach, with several practical implications for RC users. First, the ISEP clarify why a stirrer with good efficiency in an RC will display a lower efficiency in a larger RC, explaining in quantitative terms why a larger stirrer is often necessary if a target stirring efficiency is required. Second, a stirrer can be characterized in any RC, obtaining the same ISEP, thus allowing a direct comparison of the performance of different stirrer designs, unbiased by the RC features, simplifying the identification of the main physical mechanisms responsible for the stirring efficiency. Finally, since the ISEP can predict a stirrer efficiency in other RCs, an optimal stirrer design can be straightforwardly selected from the ISEP of previously tested stirrers, avoiding renewed testing of multiple stirrer prototypes.