Above FL220-250 you hold at green dot (approx. 220kts) and this is the managed hold speed. As you descend the green dot reduces but the managed hold speed will maintain 220kts until it is green dot +25kts, when it will also start to reduce. Green dot below FL220 reduces so the 380 can maintain being a Cat C approach aeroplane and is no longer a true green dot speed, hence the up to +25kts when low.