Yeah, I can see the problem -it's actually not tailored well in the back. The back darts need to be tailored in to curve to fit YOUR figure. If that means taking it to a tailor...well, that's better than having it fit unpleasantly I suppose. Padded or not, it's not fitting in the back and the easy solution is getting a pro to take in the center back seam and back darts. If you tell them you want it more form-fitting, they should get the gist.
Founder and President, Madison Area Costuming Society, a chapter of the International Costumer's Guild
Strange Land Costuming - www.strangelandcostumes.com