I've been sucessful with a couple of dend keikis, following essentially the same formula. I give mine a good shower every three days. Maybe the misting isn't getting enough moisture to the plant.
Otherwise it sounds right. Mounted, they'll dry out faster and so will need to be watered more frequently. Just follow the rule for that particular plant (whether or not it wants to dry out between waterings and to what degree.) Good luck!
Julie