I had a chance to browse through the forum on my downtime today, and Angie's thread on volume as well as Maya's post with her beautiful dress made me wonder why volume works on some curvy hourglass bodies, but not at all on others - specifically, mine.

Here's a visual illustration for you. From straight on, a sack dress is okay on me but not great. From the side, I look as if my entire torso sticks out as far as my breasts and butt all the way around. And no, this dress definitely did not come home with me.
(Compare to this side view in a very fitted dress, or this one in the Nine West dress.)

It's not just one voluminous dress that doesn't work on me. My profile looks just as wide and blocky in any other sack dress that I've tried, or tunics or tops that aren't fitted/structured (like this one, when it wasn't belted.)
(Edited to add: the above dress is a very drapey/not stiff fabric, and I experience the same problem in sack dresses with less volume - except that I look blockier from the front as the dress would fit closer around my hips - and regardless of the length & shape of the neckline.)

I'm perfectly happy continuing to define my waistline rather than surrendering it, but I'm also curious as to what makes the look fail on my figure. What makes a voluminous dress work on some curvy hourglass bodies when it doesn't work on others with a similar body type?