A system for filling a variable reflectance vehicular electro-optic element assembly (such as for a rearview mirror assembly) includes a front substrate, a rear substrate and a perimeter seal disposed between the front and rear substrates. The perimeter seal spaces the front and rear substrates apart and forms an interpane cavity therebetween. The perimeter seal has a gap between terminal ends of the perimeter seal to provide a fill port for the mirror reflective element assembly when the front and rear substrates are mated together. The fill port allows an electro-optic medium to flow therethrough during the filling process. During the filling process, the front and rear substrates are fixtured in a chamber with the fill port disposed at an upper portion of the front and rear substrates, with the filling process being one of (i) a gravity feed filling process and (ii) a pressurized filling process.