part of the problem as I understand angle in C2. is that what your looking for is relative angle to the ship, but angle itself is always going to be determined based on angle that 0 is always point to the right.
If your relative angle math doesn't come out right your going to get some strange results or no result at all. This is why I suggest the easy way. It increase your object count, but it is easier to implement.
sorry. But I spent about 20m tinkering with the method you want. I decided I didn't want to pull out the calculator and figure out relative angle trig when there was a vastly easier way to do it.
Go with which ever way you want, but don't forget that angles are -180 to +180. Where as your post only looks like it's going from 0 to 180.