I haven't tried one up top, but on the bottom, it will bump into the HD cage unless you angle it across the case.
Illustration of case bottom with light: [\]
It's fairly close, though, so you may be able to squeeze the plastic tube under the edge of the HD cage.
Mine is mounted vertically in the back corner, where it lights the case nicely, but I don't have to see the blinding tube itself.
I'll take a closer look when I get home, and see how it fits against the top of the case too. (I have it entirely stripped anyway, going to paint it this weekend.)