I have figured it out. Allow me to break it down for anyone who comes along in the future.
Basically, this widget was (is) a building block that I plan to reuse. That fact is what ended up hurting me here.
To make a longer story short, the issue is that despite a size box, if you put this widget onto a different widget, it will fill the space given, unless you have something present that ‘blocks’ it to limit the space.
The solution? Something invisible that sits and the bottom of the container that works solely to enforce the space restriction…
This configuration allowed the editor UI, and what shows up when I add this widget elsewhere, to match..
Hope this helps someone out there, and thank you to those who gave me ideas to run with that led me here.