I have purchased a [Nutri-Q 34360 Healthy Eating Egg Boiler][1]:

> How does it work? - The eggs are cooked through hot steam. The instructions will guide you on the amount of water that is required depending on the quantity of eggs. 

It comes with a little measuring cylinder for the amount of water to add which has gradations that look something like:

    Hard boiled
    - 1
    - 2
    - 3
    - 4
    - 5
    - 6/7

    Medium
    - 1
    - 2
    - 3
    - 4
    - 5
    - 6/7

    Soft
    - 1
    - 2
    - 3
    - 4
    - 5
    - 6/7

I understand why more water is required to hard boil eggs compared to medium cooked eggs (they need to be cooked longer).

However, I don't understand the gradations within each range (the number of eggs to be cooked).

Why does, for example, cooking 1 medium egg require **more** steam than cooking 3 medium eggs? Surely it should be the other way around?

Can someone enlighten me?

Photo of the parts:

[![enter image description here][2]][2]


  [1]: https://www.amazon.co.uk/Nutri-Q-34360-Healthy-Poaching-Stainless/dp/B076F577M6
  [2]: https://i.sstatic.net/8NyiO.png