The potting mix looks great but half a pot of soil is not much space for water to sit through the day. The roots are not exposed enough to be a problem but a little extra soil will reduce evaporation from the root zone and also add some extra spaces to hold a little more water. I would not fill the pot completely. Tridents love to put out new roots wherever the trunk is buried and those new, upper roots can quickly thicken the trunk and give inverse taper.
Just increase water frequency and maybe an occasional soak in a tub of water to make sure it gets properly wet once a week or so.