We use these particle sizes because the mix promotes good drainage. For adult plants or long petalled Phrags. we replace the 8 parts seedling bark with 4 parts Medium size bark and 4 parts seedling size bark.
Our Phrag. d'alessandrois - adults or seedlings-don't sit in water but are watered twice a week. Our Phrag. besseae are watered every other day, or sit in water depending upon the size and time of year.