I just had a thought so I had to write it or I would forget about it.

When you tie in marabou or hackle, if you want to be able to control how wide it spreads why not use a bead. Once the marabou is tied in, slide a small bead on the hook shank to the point where it forces the marabou to flair out just as much as you want. This can make it flair just a little or could make it stand straight out.

I know I will have to tie some now but had to put out the teaser to see if anyone does it before I do. :D