the first thing you have to understand that the small cell is not the natural sized cell for European honeybees
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According to everything I have seen with my own eyes, and read on many dozens of sites 4.9 IS the average cell size for European Honeybees, if they are left to their own designs.
Baudoux in 1893 made bees larger by using larger cells. Pinchot, Gontarski and others got the size up as large as 5.74 mm. But AI Root's first foundation was 5 cells to an inch which is 5.08 mm. Later he started making it 4.83 cells per inch. This is equivalent to 5.26 mm. (ABC XYZ of beekeeping 1945 edition page 125-126.)
Keep in mind that "normal" foundation is 5.4 mm and natural cell is between 4.6 mm and 5.0 mm.
The size of the hexagon shape on honeycomb foundation was artificially enlarged by the beekeeping industry in the early 1900s. This change resulted in a bigger bees that could collect and carry more nectar for each foraging flight.
True feral brood comb will often measure in the range of 4.6mm to 5.0mm.
ALL of these are from different sites, I could go on for quite a while. When its warm enough I can pull a frame of larvae and lay a ruler across it to take a picture to prove the point. I have foundation-less so the bees are not guided in any way to produce larger or smaller cells. ALL of my bees started out on "normal" RiteCell plastic foundation, and through rotation they were given empty frames. The very first WORKER cells they drew out were around 5.1, which is smaller than the RiteCell 5.4 mm comb. As more foundation-less comb was dropped in over time, they made smaller cells in the center of the frames. Of course, the first cells they drew were drone comb, and I was terribly disappointing, until I realized it was drone comb. They had a hayday on a couple frames, then got down to business. I make no claim that it helps Varroa etc, Only that left to their own design that they DO draw smaller cells.