It fits much better now. (This post is REpeated, with all new pics and words, as I have eaten the old ones.) ETA: I have deleted the photos from this post. I widened the button bands in an effort to make it wearable, but I still don't like the sweater. Below is a long explanation of my problem. In summary, the front is too small.
If you remember, I was confused about size selection for Mr. Greenjeans from the beginning. I knew the schematic indicated the size small, at 36.5 inches, should be a pretty good fit. However, the designer responded to a question posed about sizing. She said if you wanted to wear the sweater buttoned, you should knit a size larger than you normally would.
I just had no idea how small a sweater this is when I first saw the pattern. It's actually more of a bolero, or cropped cardigan. That's why it doesn't take much yarn. I should have realized that what attracted me ("Look, a cardigan from less than 1,000 yards!") was actually useful information about the type of sweater, not some magic performed by the designer. I know designers aren't magicians, just thoughtful hard-working knitters who are brave enough to publish their patterns.
If I were to completely knit my Mr. Greenjeans over, I'd cast on more stitches, either using the number of stitches for the size medium front with the size small back, or calculating the number needed to produce a size 38, in between the small and the medium.
Rather than ripping out the entire sweater and knitting it again in the proper size, I decided to reknit the button band. Wider button band, different button. Not a good match, but ok for now. Button shopping is on my list of things to do after the holiday.