Our initial hypothesis was that the observed isotopologue profiles ought to be correlated with the strength of the interaction between the directing group and the iridium centre; it was proposed that substrates with stronger directing groups would exchange less rapidly and therefore would undergo two isotopic labelling events before exchange with unlabelled substrate. Herein, we delineate the quantification of the isotopologue distribution as a function of reaction progress for eight substrates, representing a range of Lewis basicities, which, in turn, delivers a deeper understanding of the influence of directing group on the balance between substrate binding and C-H activation (Scheme 1(c)). Additionally, we have deployed DFT calculations to examine the underlying processes in a level of detail that complements our experimental studies.