[RbnJrg]

Tables have a drawback for the structure you're looking for. In many readers, the rows of a table do not break, and thus, if the dialogs are long, you can find many blank spaces because one row doesn't fit in the current page. Maybe the epub I attached in my last post where I fix an inaccuracy you made with the first two cols with the layout based in paragraph, it could give you a better aproximation to the ideal solution. Besides, you mentioned flex-boxes; I think that a grid would be better in this case than a flex-box (of course, you will be working under epub3).