your 1080 is most likely h.264.
like I said, try setting your proxy to prores/dnxhd which are smart codecs, then instead of rendering directly to
mpeg, render to a digital intermediate, important key here – (rendering with your proxies, not originals!) like cineform/prores 444/dnxhr or even TIFF sequence(that way you don’t have to start render over from scratch if it crashes) then re-render your intermediate into a final delivery mpeg2.