|Perfectly sewn lapels add a professional touch to your tailored jackets. Unfortunately notched lapels, and peaked lapels, are the hardest type of collar treatment to sew correctly. When the lapels aren't sewn properly, the upper edge of the lower lapel will appear scooped out. This unattractive, concave shape resembles a lobster's claw, as seen in this photo.
To get a perfect lapel such as the one below
Jackets for Real People recommends that you compensate by sewing the top edge of the lapel's seam in an convex arc just above the lapel's straight seamline.
But I think it's easier to adjust the lapel's upper seamline directly on the pattern, as the photo posted below shows.
Note that I have marked the original straight seamline with a Sharpie. The convex area I added lies above the black line.
It's better to build in slightly more of an arc than you need, since you can easily trim it down.