Ignoring the case of damaged or poor quality cable with non-homogeneous electrical properties, distortions caused by a coax happen at the ends due to impedance mismatches between transport and cable, and cable and DAC. These induce reflections which can affect the digital waveform, therefore affecting jitter in the DAC clock. The length of cable is essentially irrelevant unless you are talking about runs long enough to severerly attenuate the digital signal. Here again, for a high quality cable, that loss per meter is negligible for the frequency ranges involved with SPDIF signals. I can't think of a good reason why you'd see any difference between well made 1-meter and 2-meter coax cables.
