Organic electrochemical transistors (OECTs) are based on the doping of a semiconducting polymer by an electrolyte. Due to their ability to conjugate volumetric ion penetration with high hole mobility and charge density, polythiophenes bearing glycolated side chains have rapidly surged as the highest performing materials for OECTs; amongst them, p(g2T-TT) is amongst those with the highest figure of merit. While recent studies have shown how different doping anions tend to affect the polymer microstructure, only a handful of electrolytes have been tested in mixed conduction devices. Our work provides an atomistic picture of the p(g2T-TT) -electrolyte interface in the ‘off’ state of an OECT, expected to be dominated by cation-polymer interactions. Using a combination of molecular dynamics simulations and X-ray fluorescence, we show how different anions effectively tune the coordination and chelation of cations by glycolated polymers. At the same time, softer and hydrophobic anions such as TFSI and ClO4 are found to preferentially interact with the p(g2T-TT) phase, further enhancing polymer-cation coordination. Besides opening the way for a full study of electrolyte doping mechanisms in operating devices, our results suggest that tailoring the electrolyte for different applications and materials might be a viable strategy to tune the performance of mixed conducting devices.