I am by no means claiming that I'm an expert here. However, when working on this pattern I did have an AHA! moment. The design ease through the bust was 1.5 inches. This meant that I needed to add 4 inches in total width to give myself 45.5 inches (converter to metric here).
This pattern, the cowl tank from Simplicity 2345, has a self facing on the cowl. Its basically the front pattern flipped up and mirrored that you just fold over. It comes down below the bust and solves the problem of having to finish the front neck seam. Kinda awesome, actually. So, I cut the self facing off and started with a y-bust dart.
|Y-Bust Dart, Yellow Like important later|
|Fun with arrows.|
|Here we rotate the side dart closed, opening the dart in the cowl.|
At this point, what I did was cut it off at the red line. Then I put the facing on top, lining the under part of the arm-scythe up and marked where the facing would end, drawing my line across there. I then flipped it over after tracing the rest of the pattern and traced the new self facing as one continuous piece.
I'm sure this could work for knits and non-knits. In fact, you could even split the difference in darts if you wanted. In wovens and more stable knits I have no qualms with adding a side bust dart. Shaping is always a good thing!
And that's it. Let me know if you have any questions!