Kitchen Vessel

In a kitchen utensil designed to steam boil eggs, why do we need less water to boil more eggs?
My friend has Domestic cooking apparatus that putni a little water on the bottom and the eggs are at the top does not touch the water on a shelf – the vessel is then sealed and turned the eggs cooked to perfection. You need less water at the bottom to boil eggs and more – why is that? p. ex. http://www.tchibo.co.uk/is-bin/INTERSHOP.enfinity/eCS/Store/uk/-/GBP/TdUkDisplayProductInformation-Start; frgnIF9_bjgnIBrFUGQtRFzqNEXKvPIeZtE sid = =? productsku = 0000629
Because it is less work. When boiling eggs in a stove in a pot of water that is warming bring to boiling water, then heat the warehouse, then cook the eggs. Steam works a little differently. Egg shells and things really have microscopic pores on them, steam (superheated water / air) can pass easily through the eggshell and cook the egg inside. This is one reason why steam is healthy foods all cooked in water.