The manual says 90 degrees... others say just as long as there is a significant angle.
Here is a thread where some guys are discussing it.. a little heated at a point but there are good pics.
The first thread
http://www.helifreak.com/showthread.php?t=196544
and the follow up....
http://www.helifreak.com/showthread.php?t=199462 (I believe you will need an account to view posts).