I think the main problem, at least to me, is the concept. Here you're looking down at a tower in the clouds. That already gives an amazing scale of height, as not only are their clouds surrounding this tower, meaning it is far above the clouds... but the angle of the tower gives the impression that we're looking down at it... from high above. And we're doing so from a cliff, that I would imagine has to be a lot higher than the tower itself.
I think the idea would tell a much better story if you were looking up at the tower instead of down on it, which is pretty much killing whatever impression you're trying to give this tower in the sky. That would though, require a complete reworking so I wouldn't be surprised if you denied this crit. I think a simpler fix would to make the tower at the same height as the cliff itself, so that we're looking towards the tower, instead of down at it.
