My two cents on what I was told it had to do. Someone else would probably know the best.
“Quoting from notes taken in a recent class”
The "critical wind azimuth" has to do with the amount of tail rotor power/authority available to maintain directional control and TOT limits (TOT - wind blowing exhaust gas back up the pipe making it hotter).
Aircraft are certified to have demonstrated adequate yaw control in certain conditions - POH.
When winds are encountered from the given "critical wind azimuth", they exert a force upon the aircraft fuselage and tail section. The larger the more force applied.
If the tail rotor has very little or no additional power left in reserve (Area B of the hover performance charts e.g. full left pedal, high power setting, max gross, a nice hot day (not for those in the UK 
) at altitude below ETL) the force will cause the aircraft to yaw.
With no or very little power available to the tail rotor, one is unable to stop the yaw allowing it to accelerate, resulting in LTE.
This was a real problem with the early 206's (this is where the image comes from), hence it being mentioned in the POH in the hover performance graphs- awareness, along with upgraded tail rotor blades - improving tail rotor authority, and change of tail rotor rigging for more left pedal - again improved tail rotor authority.
Now, this is what I was told and makes sense to me with out going it to crazy mathematical calculations of where the wind is 3” from the root of the blade at the 6 o’clock position on a overcast but pleasant morning, or
what ever.
It may be completely wrong, but who knows.
Please do not shoot me....
TGZ
Editied for my poor spelling