Problem with Fiber is ...being closer to your eye it would haze, distort or completely blot out the fiber sight pin I would think.
I've been looking around since Rack mentioned the difference in defractio. of light from indoor to out in another thread.
I read a very in depth article on how a crosshair-type peep negates defraction and is excellent in low light. I had one on a bow I gave to my brother but never really used it in low light so...it was lost on me.
I did track it down again though and will be putting it on and giving it a go. Not exactly what your looking for but might be worth checking out anyway