New size for Facebook Cover Image

I don't think anybody ever informed the members that the size for a cover images had changed. I discovered this morning when I was posting the image for our stereogram page. 31 pixels shorter in the width!

Quote:

---

Displays at 820 pixels wide by 312 pixels tall on your Page on computers and 640 pixels wide by 360 pixels tall on smartphones.

---

Facebook have this annoying habit of changing image sizes without notice. I don't understand why? 31px of the image width. WTF?

I think it was to be in proportion to a smart phone screen but those are all across the board as well.