A person's positioning on the grid can actually be changed by clicking the little cog/gear icon in the top-left of any of the groups (which cog you click is arbitrary).
That will then allow you to click & drag people around to reorder them. Once you have everyone in the order you prefer, find that area where you first clicked the cog/hear icon, and click "Done Ordering", which will save your changes and propagate them through future months.
NOTE: If you drag someone to a different group altogether, this actually changes their group assignment from that date forward, just like if you were to go to the "Assign People to Groups" page and re-assign them there.
Demonstration VIDEO: https://cl.ly/773ceb04217f
That will then allow you to click & drag people around to reorder them. Once you have everyone in the order you prefer, find that area where you first clicked the cog/hear icon, and click "Done Ordering", which will save your changes and propagate them through future months.
NOTE: If you drag someone to a different group altogether, this actually changes their group assignment from that date forward, just like if you were to go to the "Assign People to Groups" page and re-assign them there.
Demonstration VIDEO: https://cl.ly/773ceb04217f