Part of it is Russian tanks really are smaller than German ones. Russians had the smallest tanks in the war, Germans had the biggest, so there's gonna be some size disparity. For example, the IS2 was only about the weight of a panther and it actually had a smaller frontal profile (width x height), and the T34 was a very small tank too. Even now Russian tanks are a good deal smaller than US and American ones (fun fact: the t90 weighs almost exactly as much as a IS2 while the M1 abrams and Leopard 2 are closer to king tiger weight).