This is a sketch of a diagram to show the structure of the "subtle decrease" I uploaded earlier. The pink-highlighted section shows what is formed by the loop that is pulled through the decreased stitches.
Row 0: cast on 6.
Row 1: Purl 6.
Row 2: Knit 2, pull loop through 2 stitches. Enlarge the loop. Using loop yarn, knit 2.
Row 3: Using loop yarn, purl 2. drop loop yarn, pull free end of yarn to tighten loop. Purl 2.
Row 4: Knit 4.