The light will be greatly reduced out at 80cm, what you want is 25 or 30 cm. That's the problem with big cfls IMO - you can't position them into tight places. But since that's what you have I'd try to move things around as much as you can, think about maybe clamping it instead of hanging it, and find the spot where it is within 3 in of as much foliage as possible but no closer than two. It's like a jigsaw puzzle, I know.