|When you are making a hem on a convex curve, which is what you have with a shaped shirt tail, the bottom edge will be somewhat longer than the hem stitching line. Here is my quick (and dirty) method of making a shirt tail hem: serge just below the hem line using a zero differential feed setting until you get to the curved part of the hem. At the curved part increase the differential feed. This will draw in the cloth on the portion of the cloth to be turned up allowing you to stitch the hem without getting puckers on the turned up portion.
I've also used this method when doing a quick hem on a neckline which I serge and turn, changing the amount of the differential feed as the neckline curve changes.