Having a low overhead for a beardie or any lizard that requires overhead heat and UV makes it difficult to properly meet their requirements. When the cage is so low your basking spot is more concentrated, which means that it gets hotter in a smaller point, so one its hard to provide a basking spot to cover he length of the lizard and if the heat is more concentrated it has the potential to burn them. Bearded Dragons will climb if they are provided with proper branches, ledges, rocks, and space.