The original width of DD had to be reduced as the first DD rake of India i.e. the HWH-DHN DD with its original width was scrapping all the platforms. During trials, it was found that the coaches were having scratch marks just below the lower level windows which was due to the scrapping of the platform edges at higher speeds.
AS far as the height is concerned, I think it is 6" to 9" more than a normal LHB coach.