scattered (grains of rice), mixed
糝 centers on the idea of small particles dispersed among other things: rice grains scattered or mixed into a dish, or more broadly things blended together in a loose, granular way.
糝 combines 米 (rice) with 參, which likely contributes the sound and the idea of mixing or scattering. The exact historical development is uncertain, but the phono-semantic structure is plausible.
Rice 米 is scattered and mixed together with the complex right side 參, like grains being stirred into a pot. The many strokes on the right suggest the chaotic, scattered arrangement.
For サン, picture scattering sand (サン) into a bowl of rice: sand -> サン, and the grains mix together.