Hi @ryan, for this technique you actually need two blueprints - one for the creation dialog and one for editing the page.
You can see a complete working example in my Open Course Hub skeleton…
Create Admin Panel Button Bar items:
Add item blueprint (note file location):
For editing a page, you would place the page blueprint in the usual spot, your example for a modular blueprint looks right assuming MyTheme is the active theme. Here are a few more examples:
Hope the above helps,
Paul