When I create a Facebook open graph image it just works and nothing changes six or twelve months later. I save the file at 1200x627 and it looks great.
When I create a Twitter card image though it can look fine, but then I come back a few weeks later and the image appears cropped. This is visible for example if you see the top pinned image at https://twitter.com/gwdesignuk
This looked absolutely fine when first created in January, following some extensive research to find the right dimensions, yet I look at it now and the image has been cropped on the sides. My latest tweet also shows a cropped image and this is the same file dimension of 1600x640, which worked perfectly before.
I would just really like to understand what is going on here and find some definitive information on correct sizes that will work on all devices. At one time I seem to recall that twitter card images should be square and it looked great, but then they suddenly appeared cropped as well and I seem to be going round in circles here constantly updating twitter card images. There is a lot of conflicting information about this on the internet.