Could you elaborate on this? I love figure-8's but can't find use for mine besides long descents :/ I have been thinking more than I care to admit about incorporating them into my rigging setups though, I've stopped using pulleys entirely (excepting mechanical advantage setups, I'm a fan of pull-overs when possible!) and am using friction-rings, the wide type not thin like o-rings although where possible I'm adding my double o-ring false-crotch as a 2nd 'equalizing' top anchor, usually there's not a great spot so I'll add it where I can if-possible even if it's just there for some extra friction and line-direction....but the 8's....I've been thinking to tether one by the basal anchor and run the line through it, giving a fixed-friction almost like a portawrap only not-adjustable (on-the-fly at least), but your using it at the high point intrigues me because I keep thinking you want to keep any real friction away from the top (to ease stress on the top anchor, as well as to have a good amount of rope-in-system before resistance is met)
I understand the idea of friction at the top causing more stress on the anchor, but the reality is the opposite. If there is no vector force multiplier in your rigging system there will be less stress on the anchor...more rope in the system can be good. However, in a good dynamic system the amount of rope prior to canopy device is moot because there will not be a significant shock load in the system....granted this is theory and good groundies are often hard to come by