I also have Q on yin&yang, but I'll adress your Q first. See page 3 where the pic shows the back with a "gash" through the piece? You are already sewing shorter fronts to a longer back. By making the piece longer, it will just be longer! You may want start with more stitches than recommended to adjust the angel of increase. How wide do you want it to be at the bottom? What will be the drape effect of your knitted yarn?
My Q is in regards to interpreting the pattern instructions. Throughhout the booklet, when shaping shoulders it states, "BO # sts at armhole once, the BO # sts once."
What does this mean to BO once? Aren't I BO total of # + # sts?