[Trigger] quick question about creating units with facing degrees

[Lumograph090]

Basically what I'm trying to do is create an ability based off Shadow Strike that when used will then create a dummy unit behind the target of Shadow Strike and then cast a shockwave hitting the units behind the targeted unit.

Here is my current trigger. I just need help figuring out how to set up the facing degrees so the dummy unit is created behind the targeted unit.

Arcane Blast
Events
Unit - A unit Starts the effect of an ability
Conditions
(Ability being cast) Equal to Arcane Blast
Actions
Set AB = (Unit-type of (Last created unit))
Unit - Create 1 Arcane Shockwave for (Owner of (Casting unit)) at (Position of (Target unit of ability being cast)) facing 90.00 degrees
Unit - Set level of Arcane Shockwave (Battlemage) for (Last created unit) to (Level of Arcane Blast for (Casting unit))
Unit - Order (Last created unit) to Orc Tauren Chieftain - Shockwave (Position of (Target unit of ability being cast))
Unit - Add a 2.00 second Generic expiration timer to (Last created unit)


I've tried this trigger out however setting the facing degrees to 90 just does not work haha, I'm going to keep messing with the facing degrees, however I know I can't just simply use a facing degree because unlike the facing of a target unit which will always be a variable my set facing degrees will not. So even if the unit is facing at an angle of 60 my secondary dummy unit will always be casting his ability at a facing degree of 90. =(