"Edit media," facebook thumbnails, and aspect ratio

This is something that’s always confusing to me. I would like to use a landscape image as my featured image, so the image that displays on my front page fits my theme. But when I share the link to a post on facebook, the landscape featured image ends up cropped in what seems to be an unpredictable way (possibly 4:3?).

If I click on my feature image, select edit image, and go into the edit media screen, there is an option to edit thumbnail settings. If I apply changes to thumbnails only and crop to 4:3, does that mean I’ll be able to keep my landscape featured image for my site but also display a usable 4:3 thumbnail image on facebook when I share the post?

And also, is 4:3 a safe bet for a thumbnail aspect ratio on facebook?

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