My fixtures are bigger than my cage also and what I do is run it diagonally instead of straight across. I put it in the middle of the cage on top of the screen and run it on a slant and it fits perfectly then instead of hanging over the edge..
It's not a good thing or a bad thing, necessarily. It's up to you if you think it's annoying that the hood hangs over the cage or if you don't care at all.
Personally I always have to turn mine sideways anyway.