Easy mistake to make so no worries. Usually, the flavor descriptions in the devotions are actually good tipoffs for where the skill where be centered. E.g. Maul’s description reads “Maul nearby foes” (so implying the radius originates from you). Same for others such as Aetherfire (“erupts at your target’s feet”), Witchfire (“erupts from your blows”) so that’s not centered on you, etc.
If there’s no specification then it’ll just appear anywhere the proc hits, e.g. Torch/Magi.
As for taking full points in Nightblade, the stats you get are also helpful yes. I just wish Blade Spirit would do anything in this case other than being a 1-point conduit for a devotion, though it’s just wishful thinking.