[PapaBear]

I think Mike has an excellent point.
A plain colored Koi has the need for bulk in order to command attention be it Chagoi, Kigoi, Benigoi,... That type of body conformation adds the impression of strength which compensates for "plainness". They are more about strength than graceful art.
A boldly patterned Koi like an old style Showa or Utsuri needs a massive frame to accomodate the massive look of it's pattern. Kindai Showa and Sanke on the other hand seem to look nice even with a slightly more modest frame.
Modestly patterned varieties like a typical bekko or a kohaku with a gentle pattern type look good with a narrower torpedo frame because the frame and pattern compliment each other as to scale.
The Kohaks with larger patterns tend to have bulkier frames (if we judge them to be attractive), also as a result of the scale of frame and pattern complimenting each other.
None of this is based on any expertise (of which I have none). Just casual observation.
I'd be interested to get the impressions of others and especially from a few experienced breeders and judges as to how far off I may be. (C'mon JR, am I close or just confused?)