Some of you may struggle with a rounded upper back.  You might have a similar shape as this.
And if you do, a curve such as this will definitely require a center back seam to help shape and conform the fabric to your contours.
Then, cut through center back up to the pivot point and spread the center back open.  You will likely need to guess approximately how much to spread each slash line open.  If you've sewn a test bodice without this tune-up, when you put it on, you should be able to measure from the neck stitching line of the bodice up the distance that you will need to spread the pattern in order to cover and shape for your neck curve.  In this situation, it was about 1" that was required.  Therefore each slash was spread open 1/2".  If you'd drawn 3 slash lines, you'd spread each open 3/8".
Let's look at what you should do to your pattern.

First, draw at least 2 or 3 horizontal slash lines starting at center back and going to the armscye seam allowance.  The seam of the armscye will become the pivot points.

And once the pattern has been spread open as shown, then you must add 5/8" (1.5 cm) seam allowance to center back.  This does mean you'll have a seam in CB for all your garments, but it's better to have it fit properly than to not cover up to the base of your neck or have drag lines coming out from the curvature of your back.
Resources
Rounded Back Fitting Tune-Up
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In addition to curving the center back seam, you'll likely notice that we also added back shoulder darts.  They definitely help too.


Here's a video on the rounded back and adding the shoulder dart.  You might want to watch it, particularly if you've never seen this process before.
And there is an article in the Sure-Fit Designs Learning Center to help you achieve the exact steps for adding a shoulder dart.  http://www.sfdlearningcenter.com/Adding-a-Shoulder-Dart.html