The dress tends to shift around when worn. If the front tie ends are tied more tightly, that helps reduce the shifting and hold the dress closer under the arm. The downside is that it also tends to make those upper edges of the side extensions sit away from the body.
This form has a very different hip shape (more of a "bustle") that really affects how the dress hangs.
The back -- tips of the underlayer can be seen, along with the edge of the facing (but that's more obvious on the contrasting color of the form). There are fisheye darts on the back, but they add only a moderate amount of waist shaping. The dress ripples down CB because the adjustable form is open there.
To make the front neckline stop gapping, I added straps from the shoulder seam down to the back underlayer. (Before I did that, the extra weight of the larger front/back underlayer piece was pulling the shoulder seams forward, causing the gapping. This helped redistribute the weight.)
It's also apparent here that the top edge of the underlayer is not very fitted at all, and that the two back halves hang open below the closure. Unless some kind of support is given to the top edge, this back underlayer will tend to drop down, which is most of the reason for those edges flaring apart (the other reason being that the form has a very curved rear). If I hiked up (shortened) the straps to raise that upper edge, it would become even looser and really start to show as bulk under the outer layer, unless I also added a lot more dart shaping.