Put it this way.
The last (fourth formless) achievement is "neither-perception-nor-not-perception ".
How one gets there, is by jumping the nidānas backwards.
So namarupa is a somewhat "deeper" level behind salayatana; but mostly the level "before",and a more "refined" level (MN 59).
To arrive at knowledge from ignorance, the process gets grosser and grosser along the nidānas. (This is, by the way, a constant in Indian philosophy - sthūla bhūta).
Once one is "knowledgeable" - that is to say that once one have understood that this is just dukkha; then one has to escape backwards.
I explained how one gets to dwell (back) in namarupa nidana - that is to say to leave the kama-loka (salayatana) for the rupa-loka.
The next step is to embark towards consciousness - and viññāṇa anidassana https://justpaste.it/6373k
To do that, one transcends form and space.
Then viññāṇa anidassana takes us to the realm of nothingness.
The dimension of neither-perception-nor-not-perception is the realm where one sees nothing more of the dharman of paticcasamupada.
ध dha (or √ dhā) - √ मन् man - somewhat meaning a "performed & established "thinking"" (dharma) [धर्मन् dharmán]
Paṭiccasamuppāda being one of these dharmán - viz. the actualisation (objectification) of ignorance.
So in that realm, one does not perceive "things" in paṭiccasamuppāda anymore (viz. perception of nothingness). But one perceives something else, not of this paṭiccasamuppāda.
I believe this to be the greatest adventure of all; isn't it?
Now let's go back to the OP (Frank) question.
Apart from the fact that I have already made him notice that he does not check for parallels (like the lousy (if not even existing) parallel on mindfulness in SA 647 (SN 48.9-10) - I have a slight remark to make on the strict parallel between Dhamma-vicaya and Dhamma-anupasssana. Not that there is none; but there is a nuance to be applied.
The 4th category of 4sp, (Dhamma-anu-passsana), is about fetching apart the noticeable phenomena, among the phenomenas (plural).
While the Dhamma-vicaya-sambojjhanga, is about pick out (select) that dhamma from the origin (yoniso vicine dhammaṃ).
Vicaya - fr. विचि vici [vi-ci]
- to segregate , select , pick out , cull TS. ŚBr. MBh.
Isn't "noticing" and "waking up" the all thing there is to sambojjhaṅgo?
√ बुध् budh
- to wake , wake up , be awake (RV.)
- to perceive , notice , understand , become or be aware of or acquainted with (RV.)
संबुध् saṃbudh [ sam-√ budh ]
- to wake up MBh.
- to perceive or understand thoroughly , notice , observe , know ib.
Parallels Frank, for Buddha's sake. That would be so nice of you.