Just look at the target. Bring the sights to what you are seeing. Exception, if in an odd position, can not see a target, unsure about drawing from that angle.....that type of thing.
I have tried it with and without a fiber. Found it was much faster with the green fiber. Just easier to track the sight. On my 2nd shot on a target, seeing the fiber drop back into the notch is much easier with a fiber.