A coaxial connector assembly (10) includes a plug (40) and jack (140) having respective inner and outer conductors matable at a mating interface. The mating interface (MI) includes a plurality of regions A,B,C of mismatched impedance having varying axial lengths defined by diameter changes of said inner and outer conductors of the plug (40) and jack (140) between respective dielectric bodies (50,162) thereof upon mating. A reduced diameter portion of the plug's outer conductor (52) inwardly from its leading end corresponds with an increased diameter of the plug's inner conductor (46) and is engaged by leading ends (176) of spring arms (170) of a reduced diameter leading end of the jack's outer conductor (160). The leading ends (176) of the spring arms (170) engage the inward surface of the reduced diameter portion of the plug's outer conductor (52) within a range of axial locations accommodating variations in the locations of the plug (40) and jack (140) upon full mating. The reduced diameter portion can be defined by a conductive sleeve (80) force fit within a front shell (52) forwardly of dielectric body (50) containing inner conductor (46) of the plug (40) until its leading edge (88) coincides axially with a shoulder (78) of the plug's inner conductor (46) between the pin contact section (62) and a larger diameter body section thereof.