So, the up-conversion 1080p DVD avi is just a little smaller in scale than the 1080p BD avi. The DVD avi is letter-boxed, while the BD avi takes up the whole screen with with small black bars on the top and bottom.
Sony Vegas might allow a little zooming in, but that would likely decrease the visual quality more. I'll look in Video Enhancer and see if I can crop or scale up just a little bit more to match the BD avi.