Potatoes - how deep?

I have tried to find the how deep thread,[but can't find it so I am updating here
I prepared my second pail for growing potatoes today by putting a scoop full of soil in the base then using a 80ml. spoon I added a heaped spoonful of chicken pellets     mixed both together then placed in the potato,     and covered with a 7inch pot of seaweed      along with a 7inch pot of leaves,     both mixed together before being added to the pail