This is a dress work page from the "Sew/Fit Manual".
On the dress back, I have drawn a line where the waist would be on the pattern. This is the line that goes through the waist dart from left to right. I have also drawn a line from the waist marking to the shoulder. This line should be outside of the waist/hip dart.
Here I have drawn a second on the armhole side of the line that was previously drawn from the waist to the shoulder. The instructions from Fast Fit stated that this should be started at 1/2" and if you need more you can make changes in 1/4" increments. These two lines will form a tuck in the pattern.
Although it is a little hard to tell, in this picture I have cut the waist line to the waist-to-shoulder mark closest to the waist/hip dart.
Here I have folded the pattern on the first drawn line from the waist-to-shoulder.
I have matched to the drawn lines in this picture. Note, the drop in the slight shoulder line.
Next, it is time to start truing up the seams. I used a cop of the original dress to do this part. Yes, it does add the full weight of the tuck back at the waist but I didn't want to remove any width from below the waist.
Then I trued up the shoulder seam.
Here's the finished mini pattern. This alteration worked fairly well for me. I'm very happy with the dress that I made.
One last thing, note that the shoulder seam on the back is now at least 1/2" shorter than the front. No, you do not need to make an alteration to the front pattern piece. They will ease together without any problem. Just remember to put the front part with the feed dogs.