Here is the second resource developed from the thread "Introductory Soil Physics". It is a document explaining how the important physical properties in soil and substrates combine to control the amount of air and water in the pore space of soils. It discusses what a drainage layer does and how the shape and depth of the container can impact water saturations as well. It expands on some of the concepts discussed in the thread. There is no recommendation here for what one should use in their garden, rather an explanation of what your choices are.
Introductory Soil Physics 1.2
Introduction to the physical properties of soils and substrates.