From my elementary aerodynamics from 34 years ago, view the shape of the aeroplane as a series of cross section areas nose to tail. The graph of those areas should be as smooth as possible in a nice smooth mountain shape to minimise drag. Hence where the wing is, ideally the fuselage should 'waist' (impractical engineering wise). After the wing, some filleting should be used to smooth out the sudden drop in area (big fat wing root fairings or wing mounted area ruling structures-
http://www.!!!!!!!!!!!!!!/open.file/327737/M/). Those Convair 990 ones are called anti-shock structures, but I think it's the same thing.
Airliners don't allow such free expression with design as fighters, and it's with fighter design you very often see significant area ruling features. Don't know
why , but it seems to work.