This is a bug report and a feature request. The new nameplate system completely trashes group banners, which didn't have a great standard (or any standard, for that matter), to begin with.
Currently, on live, a (mostly) consistent group banner means uploading a mostly transparent picture with the actual banner in the middle. This is wasting tons of space that could be actually used to show other art or graphics on the group page.
The image scales very poorly on some parts of the site, as well.
And now on beta with the new nameplate, we see just a few pixels of the group banner. This is effectively useless now for representing a visual of your group. I've attached a picture showing some of these inconsistencies.

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