[Trevor Asquerthian] “I don’t believe that’s true. By necessity the previews must match the export (typically ProRes or DNX) and thus the rendered parts of the timeline become copies.”
Actually, if you go look into your Sequence Settings, you can see what your preview is set to use. Either matching your sequence or using I-Frame MPEG. They DO NOT match your export settings. The export is whatever you make it. PPro has no idea what you will be exporting your sequence to.
TC