I made a solution by moving the target, so the enemy ship never stops, and it leaves the screen.
But that is not good, when the player is all the way down or up the screen in the moment of storing its position, the movement of the target will alter the angle too much. I want it to work the way i imagined it, on a direction set by non-moving target.
That's only an issue if you're moving the target in a specific direction. Imagine a line from the ship, going through the target and continuing off the map. You can move the target along this line to keep the relative direction.
In this example, your ship(S) is at position (2,2) and the target(T) is at (4,5). Now you can work out the direction(D) using the formula D=T-S (Direction = Target - Ship)
4-2 = 2
5-2 = 3
This gives you the direction of (2,3) 2 across the X axis, 3 across the Y axis.
So if you added (2,3) to your target vector (4,5) you'd have a target of (6,8) highlighted in blue.
You'll notice that if you were to run that formula again with the new target position relative to your ship, it's doubled (4,6). As long as you move the target in increments of your direction Vector, it'll always be the same direction relative to the ship.
SO once you've got your Direction (2,3) multiply it by 100 (200,300) and add that to your target position. It'll still be along that invisible line, so the angle wont change, but the target has moved further away.
I'm sure there's a more sophisticated way to do this, but I can't think of 1 that doesn't use 2dPhysics at the moment.