The short rows should create a curved edge. When you work a certain number of st. st. rows, you will get a 3.5 inch long piece of stocking stitch. The 3.5 inches of stocking is not shaped, it is a plain stripe or rectangle, with no curves, work 3.5 inches of this.
The stocking begins at the same row all along the row, you will get the same measurement whether you measure from the start or end of the sr shaping. Does this make sense?