Hi there,
So we did not implement the “between” option, and the cryptic exchange there was because we added an image trace type, meaning that for images, you can now add an image trace on top of the grid lines and then subsequent traces on top of that. Hence “no longer relevant” for the image case. For the shape case, this is still relevant, as you show above, so I’ll reopen the issue.
That said, as a workaround, you could use line traces instead of shapes here, as they will render above the grid lines, and you can layer additional traces on top of them?