Image size not adjusting

The image size I'm getting in the activity stream when I use Activity+ is 150 pixels wide. I tried to adjust using:

define('BPFB_OEMBED_WIDTH', 400, true)

but nothing happens. I managed to get the image sizes to adjust by changing the default thumbnail size under the WordPress > Settings > Media page. This changes the default size for all thumbnails on the site.

Is there a way I can get Activity+ to show the "Embeds" size from the Media Settings page and not the thumbnail?