Electrical connector system

A header assembly for mounting an electrical connector to a substrate comprises a plurality of ground shields each defining at least one ground substrate engagement element (156) at a mounting face of the header assembly, and a plurality of signal pins each defining a signal substrate engagement element (158) at the mounting face of the header assembly. Each signal pin of the plurality of signal pins is associated with another signal pin of the plurality of signal pins to define a signal pin pair (142). The ground substrate engagement elements (156) and the signal substrate engagement elements (158) are positioned on the mounting face of the header assembly such that there is at least one ground substrate engagement element (156) positioned directly between each signal substrate engagement element (158) and any of the closest non-paired signal substrate engagement element neighbors.