These three points are located on the Stomach channel on the lower leg. They are used in various combinations for different applications.
Four Flowers Upper is also called Si Hua Shang 77.08. Overlaps Stomach 36, 3 cun distal to St 35.
Four Flowers Middle is also referred to as Si Hua Zhong 77.09. Located 7.5 cun distal to St 35 (or 4.5 cun distal to Four Flowers Upper)
Four Flowers Lower is also Si Hua Xia 77.11. Located 12.5 cun distal to St 35. Another way to think about this would be to measure proximally along the Stomach meridian from the hiatus of the lateral malleolus by 3.5 cun.
Four Flowers Append (Si Hua Fu 77.10) is also represented in this graphic and is on the Stomach channel as well.