I had the header 210*1100 pixels. I changed the image and it automatically changed the width to 1650. But it is impossible (I think), because the total width is 1600. I tried to re-size the pictures in many variations but can’t find out how to get the whole pic. on the website.
This is an undocumented ‘feature’. There’s some extra padding that we lost along the way and we had to include it somewhere. So the header will always be 50px wider than the width displayed by the width selector.
This is not explicitly stated but the widths are correctly displayed everywhere even though they are out of sync.