Just to try and bring a final clarification to the thought that even people standing behind the navigator can be affected, I just now got a response from Sam Stewart regarding this:
Hi ***,
The attack should be treated as having a 180 degree arc. In fact, I'd
probably only treat it as having a 120 degree arc from his front. (So
someone standing next to him could avoid it).
Hope this helps!
With that done, I personally do not think the navigator should gain a level of fatigue for every person it affects, that seems to make it a one-shot thing. Granted, it is frickin dangerous, but I frown upon any design choice that takes a player out of the fight after using one spell/power. Giving an aditional level of fatigue for every target that beats the oppossed test with 2 or more degrees however, that I find kinda plausible. Makes it not the ideal weapon against a group of psykers, or other navigators.
)