Not sure what you exactly want. But lets show you the basics, and a problem that can arise with it.
In this capx, you see a paralaxed and a non paralaxed layer.
With some imagination you see a little player with a big gun.
The gun should always point to a fixed place on the screen.
The parallax happens because of the scroll to behavior on the player.
For that we need a fixed layer to place that object on (the green cross).
Now we translate those positions to positions on the paralaxed layer.
The black cross shows the result, but is not needed.
This are the basics.
But as you see, and maybe that is also you problem, with a scaled layer, it is not exactly spot on.
Well in fact, it is, but it is to late.
The scroll behavior moves the layer on the very end of the tick.
So we, in fact, when we start measuring, comparing, and then set the position, we do it before the parallaxing happened.
How do we solve this ? We just do the parallaxing on the exact moment that we want it to happen.