Above picture shown us the relation of good geometry model could obtain good results when you model plastic injection plastic part. How sink mark can be captured in thick-ribbed areas. Then take a look how good mesh model was.
Sink mark is one of the most common defects on plastic injection part. The defect in plastic parts are developed when material in the region of coarse characteristics, such as ribs or protuberances, contracts more than the material in the adjacent wall. The presence of such a feature creates an effectively thicker region which cools more slowly than neighboring regions. Cooling differential speeds produce a depression in the adjacent surface known as a sinking mark.
After capturing the sink mark defects, modifying certain area especially on ribbed and boss area may needed.