I like the pot to be narrower at the base. Then the pots knock over easier but if you use enough inorganic heavy material this is not that much of a problem. This narrowing helps water back up to get a good watering. keeping a layer of more open mix at the bottom still allows good airation. This is my experience from lots of experimenting. When I repot this year all my paph will be potted this way. I am still unsure of phrags and the differences between them.