[Mivereous]

If you are right next to the NPC casting it, it starts on the same tile as them, and goes through you, to what is probably a decent length. If you are a few tiles away, it tends to start the tile closest to being in between you and the NPC, and again, goes through and continues a decent length. When a player casts it, it starts on the first blue tile, and ends on the last, as it is probably intended. At least, that's how I just confirmed it being a few times.