Kindle paperwhite covers not showing for some news recipes

[jhb-812]

When using the Calibre recipes tool to fetch news, some of the recipes do not show the cover when the device is in Sleep mode, while other recipes show the cover normally. I'm wondering if anyone knows a way to guarantee the covers will show when the device is in Sleep mode.

Not showing: The Economist, The Atlantic, TheAtlantic.com (these covers are screenshots that I manually paste into Calibre each day I fetch news from this source).

Showing normally: The Economist Espresso, Psychology Today.

Note: I thought maybe it was about the size of the photo, but The Atlantic and Psychology Today's covers are almost exactly the same size (PT is slightly larger even) and Psychology Today shows normally while The Atlantic does not show at all.