Hummm that is another one I have never heard about... a radius limit on Fade.
When ever I hit fade, the OOC icon pops up and I can't re-aggro anything by accident. You can even out-run aggro without fade, I do this all the time when running past the see-invis at the bottom of the LP ramp. About 2 seconds after you hit the waterline, you lose aggro and your OOC starts up. You can run all the way back and not re-aggro. Likewise... ive gotten all the way there (almost to the water) to find the camp I want taken and fade off aggro and turn around and run back. Getting close to the see-invis the mobs do not remember me, that is at the extent of aggro range before the automatically forget you.
Of course there is a "dead zone" where mobs stop following you but do not forget about you, that is unless they walk back to their spawn point past the "dead zone" and your OOC will start again. Running back will not re-aggro unless you pull. Of course this has nothing to do with fade, it's the same with all classes.
The only time where I have found that fade will not work, is when a mob is running from you at low health. That mob will always remember you unless you kill it or zone. It will stop running when you fade, but as you get close again, it will start running.