“How can a dhamma even be below this level when a suddhashtaka is the base unit and cannot be divided?”
Dhammā are rupa that are not detectable with the five physical senses. They are rupa detected with the mana indriya. See, #9 of “What are Dhammā? – A Deeper Analysis.”
Also see, “Our Two Worlds: Material and Immaterial.”
Dhammā are, “anidassan appatighan dhammāyatana pariyāpanna rūpan“. I need to find a reference for this particualr verse. If anyone has the reference, please post. I am providing a related reference below.
The following reference is in the Abhidhamma Piṭaka. Āyatanavibhaṅga
“Tattha katamaṃ dhammāyatanaṃ? Vedanākkhandho, saññākkhandho, saṅkhārakkhandho, yañca rūpaṃ anidassanaappaṭighaṃ dhammāyatanapariyāpannaṃ, asaṅkhatā ca dhātu.