I believe that the sentiment is that a just one small cell will invalidate the entire packet, so what might appear like a low BER can result in many wasted bits. But this is true in any system that handles large packets. If you carry 4500-byte frames over FDDI, only a couple of bad bits will cause the frame to be tossed. In other words, nothing new here. Large packets are great if error rates are very low.
Small packets are better is error rates are higher.