Thanks for everyone's help here guys.
@notnsane, add a secondary condition that is called 'pick random instance', as everytime the game cues the enemy to 'shoot' it will pick one random instance of that enemy on screen and make it be the one to fire, so the player is not assaulted by a barrage of bullets. Hope that was remotely helpful. :)
Yeah, I'm trying to figure out the maths now, and I did have a go at creating the circle, but the problem was that once created, if I tried to alter the bullets trajectory, it altered EVERY instance of that object, which didn't work, because the circle (by default) resulted in negating all movement, as for every trajectory, there was an equal one acting in the opposite direction. -_-