A sharp 90°bend is an anti-blocking device. It should ONLY be placed IMMEDIATELY BEHIND A WALL INLET OR AT LEAST THE FIRST BEND if the pipe runs on the other side of the wall to the inlet. It should also be put immediately on top of any VacPan inlets that you may have.
NB: Should you put this fitting in any other place within the system ductwork, other than those stated above, your lifetime guarantee against blockages will be made invalid.
See Page 15 of the Installation Manual below for more details.