A header assembly includes a header housing and contact modules coupled to the header housing each having a frame assembly with a signal leadframe and a dielectric frame. The dielectric frame includes mating portion extensions at a front of the dielectric frame. The signal leadframe includes mating portions extending forward from the mating portion extensions. Each contact module includes a ground shield having ground shrouds providing electrical shielding for the mating portions. Each ground shroud includes shroud walls forming a shroud cavity receiving the corresponding mating portion extension. Each ground shroud includes a shroud transition to vary a depth of the shroud cavity along a length of the ground shroud.