"Oddly, when Atari released the 5200, no such backward compatibility option was offered, confusing some consumers and hurting system sales. Atari tried making amends with a smaller 5200 system redesign and an awkward add-on module that enabled the backwards-compatibility gamers demanded. Unfortunately, this add-on was incompatible with the earlier, larger 5200 consoles without modification at a service center."

There was never a "smaller" 5200 redesign (one was prototyped, but never released, IIRC). The redesigned 5200 that was compatible with the VCS adapter had 2 joystick ports instead of 4 and went back to a more conventional RF switch design, but the actual size of the unit remained unchanged.