Wallace, we're all just winging it. The old books urge prompt replacement for failed transplants in order to avoid rank growth in the plants adjacent to the missing plant. In deep-bed planting (the technique I've adopted for tobacco), the between-row distance is ignored, and all plants are spaced in staggered rows using the between-plant space recommendations.
If you plant at 16", you may find them crowding out their neighbors for sun. I think a double row (staggered), with 21" spacing, with mowed grass in the wide isles between the beds would work well. This would allow access to the row from either side, yet still limit the available soil for the roots.
Bob