Light of Dawn is not a frontal cone. A frontal cone would look like this (pretend there are lines between the + signs connecting to the P (paladin). Note that the diagram isn't meant to show the exact angle of Light of Dawn, it's only for illustration purposes.
What we actually found was that Light of Dawn covers a rectangular area as follows:
I am curious if anyone else has done any testing like this, and what your results were.
Here's some screenshots of what we found to be the healing zone of this spell. Note that the flares were starting to go away before we got all the way around unfortunately.