see: https://github.com/cu-mkp/making-knowing-edition/issues/173#issuecomment-522142964
The issue here is that my code expects the margin blocks to follow the main block. Sorry not to have made that clear. If you move the <ab> that is middle-right to the bottom of the <div> it sits in, it renders in the right margin middle. So no code change for this fix, just need to adjust the markup.
@tcatapano - has this been completed?