Do you know how water behaves in potting mix?

This illustration shows how gravity verses capillary action of the mix to leave
a wet layer of a regular pattern, regardless of the depth of the container.
This means a shallow container will be wetter, or relatively less well drained.

This illustration shows the crocks on the right actually impede drainage
when compared with the left illustration which demonstrates the effect
of sitting pots on capillary matting, without crocks.