Unfortunately, popups on editable layers is currently broken. That's why you're not seeing any. We plan to release an update to the website early next week.
As far as configuring popups for editable layers, it's not supported. Editable layers basically have a title and description and an optional image. You get all this information in the popup. If you don't want some part, leave it blank.
It's not possible to customize the size of the popup. You can enlarge it and it will completely cover the map display. Click the square icon in the title bar of the popup.
As far as viewing popups in embedded maps, by default we switch to our mobile popup version for embedded maps with widths 500 pixels or smaller. I'd like to make this an option, but for now, it's hard coded into embedded maps.
Thanks,
Mike