I asked this same question to one of our experienced skydivers. There's a couple reasons to put the slider behind your head or under your chin - or even in your teeth. With the slider all the way down the risers, it allows the canopy to flatten out more, giving you better performance on turns and flare (or swoop). On my new 135 (god, I love that thing) - my slider actually wants to come down the risers and sit behind my head. I'll be testing it out today and let you know... Light, love and laughter, Katzeye