The validated SiD design includes an electromagnetic calorimeter (ECal) that features twelve identical trapezoidal modules with overlapping ends that eliminate projective cracks (the darker, inner calorimeter of Fig 1). At normal incidence, the ECal contains 26 X0 of tungsten alloy absorber for an extent of 13.9 mm beginning 1.264 m from the interaction point. Photons and electrons create electromagnetic showers within the calorimeter, but a small portion of the shower is scattered off the calorimeter’s edge and deflected. This is known as “backscatter”. As the shower progresses through the calorimeter, its width increases due to contributions of low-energy particles leading to “shower spreading”. These two effects are investigated here.