I got it a bit further. I can align and scale them if background image is Y 50%. But it only aligns in center of stage.
I can't figure out how to make them align and scale to the top center.
In order to get scaling to work for your symbol instance, you need to set your symbol's stage to 100% 100%. Then you'll be able to select the % of your X, Y.
Thanks for your feedback! I did that and with a few other steps got it to work.
I also found that if the sizes of the graphics where different that added complexity to the scale and making them off.
It's a bit trial and error. You basicly have to play with it until you get the result. But I got it working now.
Glad you got it working, Christian!