I have a 5V power supply that is converted to 3.3V using a buck converter. Now I want a 1.8V supply. What is the industry standard way to feed a 1.8V buck converter? Do we feed it from the 5V supply or from the 3.3V supply?

From an efficiency point of view, I understand that the most efficient way may depend on the loads. Still, on buck converters, the efficiency gets worse, generally, as Vout is further away from Vin. But if I feed the 1.8V converter from the 3.3V one, I already have the power loss of the first one, albeit maybe getting a small boon from the increased current draw if I am on the side of the efficiency curve that favors an increase in current.

Nevertheless, what is generally done in this case? Two buck converters converting from the same supply, or one converting from the other?