Trigger to drop down menu is in scroll bar

I am wanting to give learners the chance to choose from a drop down menu - I have got the drop down box appearing on a different layer when the user clicks a shape and the states of that shape are set to change depending on their choice from the drop down menu. 

It is mostly fine but some of my shapes are in a scrolling panel - meaning that when the user clicks on it to show the drop down menu, I am struggling to correctly format the drop down menu to show under the shape- as the shape position changes depending on how far down the user scrolls but the drop down menu position is set. 

Is there a way to anchor the drop down menu position to the position of the shape on the base layer? 

I hope that makes sense and have included an example