No, not a "small". To be clear, the lens is a S, medium. I personally named that lens. Isco was going to call it the Isco II again, and I told them that would be a mistake since there was already the older out of production "Isco II" with a lower performance conotation. They agreed and we called it the IIIS. "S" for smaller than the "L" of the IIIL but of the same design.
The "M" came later when Isco began making/branding the lenses for Schneider who had the tiny CineDigitar. They thought to avoid confusion in thier line they named the Schneider branded lenses "M" and "XL", which was confusing IMO, but Schneider didn't take input from me like Isco did. The Isco IIIS and the Schneider "M" are the same lens, made by the same machines and poeple, with a different focus ring. Identical size glass. Both are "medium" in size.