Why the posting order is the reverse of the grid
A profile grid is sorted newest first: the last post you publish sits at the top left and pushes everything else one place along. If you lay out nine tiles and want them to appear exactly like that, publish tile 9 first and tile 1 last. The tool shows the publish position on every selected tile and in the note under the grid, so you can schedule the posts in that order in whatever you use to publish. Changing the plan later, for example by inserting a post in the middle, shifts every tile after it by one place.