I read your article “Mystical Phenomena in Buddhism?”, really enlightening.
Looking at the scale it seems quarks qualify as having a size comparable to suddhātthakā as the most recent data would put them around 1b times or smaller (depending on the flavor) than the atom.
However you mention suddhātthaka aren’t electrically charged, which means suddhātthaka is another sort of particle possibly outside of the standard model.
By the way, where does the suddhātthaka scale come from? Is it explicitly mentioned in Tipitaka?