reason I always choose 640x272 as it is easier to upconvert to 1080p eg; 640 x 3 =1920, 272 x 3 =816.
obviously the vertical resolution is increased for 16:9 aspect etc. I also up the bitrate for the vertically higher aspects.
Also read somewhere that some MP4 standalone players only allow aspects divisable by a factor of 16 so I always try to stick to this rule when possible
still be interested in them if you ever reseed.
Forgive my ignorance just realised you were probably trying to keep the DVD's vertical resolution with your sizing.