The exploration of the Michael addition of indole to trans-crotonophenone, catalysed a diverse range of XB-based catalysts, has provided profound insights into the catalystsubstrate interaction. Electronic properties of the XB-donor and the catalytic scaffold influence the size of the hole σ, while steric effects between the XB-donor atom and catalytic scaffolding also play a critical role. CAT6, CAT7, and CAT8 highlighted the importance of XB-donor atom positioning within the catalytic scaffolding, specifically in terms of how it affects σ-hole size and catalytic deformation energy. The recently proposed π-type activation mode was compared with the more discussed O-activation mode. Remarkably, the theoretical results of the π-type activation mode align more closely with the experimental data and are thermodynamically preferred by the bidentate scaffolds and I 2 . This mode has unveiled an alternative mechanistic pathway characterised by a dual non-covalent and slightly covalent nature for I 2 catalysed Michael addition of indole to trans-crotonophenone, providing insights into the reaction mechanism of this robust catalyst. Heteroatomic bidentate scaffolds preferred the π-type activation mode due to the ability of the scaffolds to simultaneously bind to both active sites of trans-crotonophenone; the carbonyl oxygen and α-carbon. For the homoatomic I 2 , its π-type activation preference arose from its unique and relatively strong dual non-covalent and slightly covalent interaction with the substrate's α-carbon. Understanding these activation modes and their interactions is crucial for the design of efficient XB-based organocatalysts for a broad spectrum of chemical transformations.