@Anzak: Hmm, it should work. I’ve tried it out myself. Show Default Tile is set to false, right? It should be impossible to walk off the edges if there is nothing blocking PathTrace in those locations using the instructions I provided. I hope I’m not omitting something essential.
I’m guessing the collision box blocks visibility because it is set to block RangeTrace, the trace channel that checks if units have line of sight to a tile. If I am correct in this, set the collision to “ignore” for RangeTrace and it should work.