Rise Cover Photo Dimensions

I've been fussing with my image all morning and am starting to suspect that Rise is wanting certain dimensions for the cover image, not a 3:1 ratio. The best clarity I was able to get - still distorted but not nearly as badly as the other 3000 versions I tried - was with an image that was 4063 pixels x 962. This is almost, but not quite 4:1, but 4:1 was as badly distorted as 3:1 even though the image itself was slightly larger. 

Does your tech team have any insight into what dimensions Rise wants to resize to for the cover image? I've read the best practices and they say to just use the best quality image available because the Articulate image compression engine is awesome. I'm not finding this to be the case, so I would like to size it in Photoshop if possible. Attached is the image that is working the best (labelled v3005), as well as an earlier version that looks even worse once brought into Rise.

Also, can I expect that the image will clean up once published, or does it preview at the same quality that it publishes at?

Most versions looked more like this (distortion along the person and even the triangles are extremely blurry. The size of this image is 2908 x 969, which should be more than adequate but is cropped at 3:1.

Here is the image as it appears at 100% in Photoshop, to try to prove that it's not just a low quality image.