At least one hex at radius 3 is necessary for the final swing/pivot of each product. The only glyph that can go in that hex is a calcifier, and the only motion that can put an atom over such a calcifier without additional area is a pivot from a knights move away. The bonder position is forced, and the debonder is extremely awkward if it's moved anywhere else. Solving the puzzle with those constraints did not seem possible, so I'm reasonably confident 21A is min.