Unable to setChildIndex of placed movieclip in Canvas document

I was a long time Flash Developer and really loved using Flash/Animate for building quick user interfaces for simple puzzles and games. I have been attempting to do something seemingly incredibly simple that just won't work.

1. Make a movieclip with some nested movieclips, each having an instance name

2. Drag the movieclip to the stage, and give it an instance name.

3. Use mainClip.setChildIndex(object1, mainClip.numChildren - 1) to bring object1 to the front of the displaylist.

the child index of object1 does move to the front, but it does not render in front. This is not very helpful!

I have noticed, however, that if I instantiate several movieclips from the library via code, I can change their order via setChildIndex and it works as expected. But any instance named objects nested in those movieclips cannot be rendered in a different order. (once again, their indexes can be changed, but they remain rendered at the same level)

This seems to be a pretty basic thing to be able to layout pieces and change their depth. For example, imagine a board with pieces where you can click one. It would come to the front of the displaylist so you can drag it across the canvas on top of other objects. Can we no longer layout assets visually?