Lovely photo of Hubble there! Did you manage to get any more substrate in for the base? Just thinking it is quite a drop from the roof of the cage if he climbed up there and fell. That would make the bendy stick bridge higher up too as that would be quite a hard thing to fall on from a height, and would make access to the wheel easier too
It's surprising how much the substrate flattens down after you put it in. I sometimes fill mine to the brim and then it only looks 2/3 full a few days later and I'd end up putting some more in.