Nozzle location should be as parallel to the airflow stream as possible.
The nozzle angle in relation to the airflow stream is termed the "intercept angle."
According to Strader, the intercept angle should "not be more than 45 degrees, although it can be less.
Maintaining the proper intercept angle generally helps low-speed driveability and may also improve performance throughout the engine's operating band.
The lower the inlet airspeed at idle, the more critical it is to maintain the ideal intercept angle. Idle vacuum correlates well with inlet airspeed-if you have 14-18 inches Hg of vacuum at idle as read on a vacuum gauge, maintaining the proper intercept angle is not as much of an issue in terms of driveability, although there still could be some emissions ramifications.