Sir placement of the AC Coaches in the back is Signature ER style CC !! For Ex SDAH and HWH are Terminus Stations and AC Pax could get better accessibility if the Rakes are made like this ! If You Notice the More the Class is of the Coach it is pushed back Proportionately in the CC. Thats Why AC Classes are in the back side in any ER ,SER train Leaving from Howrah/Sealdah. In the Rajdhani Shatabdi the H/E class Coaches are at the Last position which makes it the first Coach in the rake to be accessed by Pax and then 2A and then 3A and so and so. :)