Zoom Docs - covers

[Caffey]

I use Zoom docs daily and find them quite useful.  Most of the time I'm not interested in using covers, but they are helpful in some cases.  I understand that I can upload custom images to use as page covers and that the maximum size is 20MB . . . but that is literally the ONLY information I can find *anywhere* about working with covers.  Is there any documentation available on this?  It is clear that images resize and scale dynamically but it is not clear how this works or any suggestions on how to create headers effectively that will look as intended at various sizes.  Is there a Zoom Docs documentation resource that I don't know about?