Controlling the order

The way to control the order in which items appear in a region is to add a digit after the first (regional) part of the customfield name. So to make the graphic come first, the two customfield names could be left-1-post and left-2-list.

Note that this also means that when WordPress helpfully rearranges the customfields in alphabetical order, this will now reflect the order in which the items appear on the page (within any given region). However, items like left-post, without any digit, are treated for column-ordering purposes as left-0-post – but WordPress will not, in this case, rearrange the customfields to reflect this.