UNDOCUMENTED MECHANICS
This is a sustained aura: only targets inside the radius carry the debuff, and it ends the moment they leave.
"Defense" above follows a diminishing curve, not a flat gain per level; the other numbers in the same block do not: -49% at level 1, -70% at 5, -80% at 10, -90% at 20, -100% at the limit. Reaching the limit takes skill level 60, gear bonuses included, so the first few points are worth far more than the last ones.