OK, first of all holy crap that's a lot of complicated maths you had going on there under the shooting AI If you can get it to work that way that's cool, I just tried my lazy way though. After adding a "Last shot distance" to the Text object, I did some testing and noted down some relative angle/distances.
The furthest you can shoot is 503 pixels at around angle 43 (where 0's the lowest angle possible, 80 the highest). At angle 0, you shoot 124; at angle 80, you shoot 169. I noted down the distances for every 10 angles from 40-80 (since I assume you want your enemies shooting into the air, not straight forward). Then for the enemies, I just used these distances, detected the distance between the 2 ships and set the angle accordingly every 10 increments of angles (adding 185, 180 cos we're firing the other way, and another 5 to get a midpoint).
Also added the Pin behaviour to your turrets and made the enemy ship a container of them; now every time you add an enemy ship to the layout it'll come with two turrets which are linked to that particular ship, which can be handy! Added another layout called "unused", which is a good place to hold stuff that only exists in containers, otherwise it can mess stuff up on your main layout as it automatically spawns everything associated with that container
As I said, this is my really scrappy lazy way, the enemies aren't 100% accurate but I think that's more realistic You can probably improve it by figuring out the neat way; ie finding the formula for the curve of the projectiles.
Hope this helps and good luck with it, I had fun playing with it!