How can I determine the location of a popup?

Sorry for the dumb question, but I just can’t figure it out. I’ve looked at this great guide as well as the documentation, but I haven’t figured out how to do it.

I know how to set position relative to an object (like aboveleft, belowright…) But I can’t figure out how to choose the “object”, the “placeholder” of which I then define the relative position. In the image this object/placeholder is the blue square or the orange square.

For example I have a button on the side that when clicked I would like to open a popup “1” under an $edit-text widget. How can I tell TiddlyWiki to open that popup “1” under that specific $edit-text widget?