[UI] Widget canvas is tiny when created by blueprint

I’ve been struggling with my interaction list blueprint not rendering correctly. I assume there’s something I’m missing in the way I’m constructing the widget.
The InteractionList widget is simply a vertical box (no canvas panel) and the size is set to “Desired.”
While the debug codepath is an acceptable alternative in this instance, I’m worried this means there is no way to create instances on the fly for use cases where the number of instances needed is only known at runtime.

InteractionList_29 (in the debug comments) was placed in the Designer and functions normally. The main branch constructs a new InteractionList and adds it to the canvas, but it appears to have a tiny canvas for some reason.

InteractionList_29 (blue), programatic InteractionList (red)

Here is how InteractionList is adding children

InteractionList’s Initialize function which calls Add Interaction

And finally, InteractionList’s tick event

I stumbled onto the solution while wrapping up my interaction system.
Apparently, widgets are children of slate objects as documented here: Slate Architecture | Unreal Engine Documentation

So by working with the slate object I was able to set the dimensions using this pattern.