Hmmmm.. great concept you have going there....
You just inspired me a great deal...I hadn't ever though of doing something like that...very nice...has a lot of potential..
As to your problem..
Are you using any kind of Helper Sprites?
I would suggest that as an option, First and foremost
They are really handy..and help conceptualize what you are trying to achieve and can even have code or events keyed into them...to assist the mechanics of your game.
Invisible helpers are basically simple sprite objects that can be any shape or appearance that help out the mechanics of ANY system...
In this case they could be Sprite representations of the Angle "Arcs" that you wish to cover...These sprites, when you create them and load them into CS2 can be set to any angle you like..so you can almost "prefabricate" your whole set up visually & mechanically first...Keeps it all unified if you know what I mean
By replicating the Mathematics of angle checking with visual guides you would have a much easier time of understanding the System
Does that make sense?
Don't forget you could always run a testing function as well by having a HUD display that has "Text" object for each angular Field Arc sprite and has it continually update on screen so that you can see exactly what relative angle is happening at any time..this would give you some proper analysis feedback to plan out your system better ...much like an on screen frame rate update but it displays the relative angle..
Your idea is a great one...yes definitely interesting approach..:)