Yesterday I joined a mithra on some mob grinding for 2 hours. I wanted to test out the heal spell called sacrifice. I stood to the right side of her and casted the spell. The spell only landed on me. The next time, I stood behind her and used the spell. This time it worked. I faced opposite of her with the monster in between us, it also worked. This lead to my conclusion that thaum's heal is a cone-shape which means it is a bad idea to use it on another member since it wont hit anyone else due to cone-shape.
Conjurer's cure is not cone-shape, its a small circle radius around where it is casted.