Hi Ekocare,
Let me pay homage to the Lord Buddha and the Dhamma he taught us and the elders who preyserved and gave us these commentaries .Any thanks only to them and blame to me.
Many thanks for taking your time to reply in detail.
your question is good and is in the right direction
because you want to see how they are different while you already found that they are related(similar).
You almost got it but probably the translation as ghana as compact and the below mentioned overlaps caused your question.
what I understood from your response is the two overlaps ,but you can see in the clarification below whether they are applicable or not.
1.you have applied “characteristic” for samuha-ghana as well as for arammana-ghana
2.you have applied function for kicca-ghana and arammana-ghana
Now to my clarification. Though it might seem like a big reply ,you can walk through the bold and see the differences and also how they are related real fast .
Those four ghanas teaching addresses common/related objective and also with different dhammas (eg:khandha,dhatu,ayatana).
I will just refer the lines through which you could get the differences/relation instead of providing lot of details which I believe you might already know.
First how they are different:
For santati-ghana: patisambhidamagga-atthakatha-227
nimittanti santatighanavinibbhogena niccasaññāya pahīnattā ārammaṇabhūtaṃ saṅkhāranimittaṃ yathābhūtaṃ jānāti. tena vuccati sammādassananti tena yathābhūtajānanena taṃ
For samūha-ghana: patisambhidamagga-atthakatha-227
samūhaghanavinibbhogena ubhayathāpi attasaññāya pahīnattā saṅkhāranimittañca vipākapavattañca yathābhūtaṃ jānāti.
For kicca-ghana:
visuddhimagga-mahatika-729
tathā tesaṃ tesaṃ dhammānaṃ kiccabhedassa satipi paṭiniyatabhāve ekato gayhamānā kiccaghanatā,
More clarity at vibhanga-anutika-229
ekappakārenevāti yathā cakkhādīnaṃ manāyatanassa paṭiniyatadassanādikiccānuvidhānato niyato ekappakāreneva paccayabhāvo, na evaṃ rūpāyatanādīnaṃ
For ārammaṇa-ghana:
visuddhimagga-mahatika:729
tathā sārammaṇadhammānaṃ satipi ārammaṇakaraṇabhede ekato gayhamānā ārammaṇaghanatā
Here sārammaṇadhammānaṃ definition can be found at dhammasanganipali-1191
katame dhammā sārammaṇā? vedanākkhandho, saññākkhandho, saṅkhārakkhandho, viññāṇakkhandho – ime dhammā sārammaṇā.
Second how they are related:
visuddhimagga-dutiyo bhago-paṭipadāñāṇadassanavisuddhiniddeso-upakkilesavimuttaudayabbayañāṇakathā-739
nānādhātuyo vinibbhujitvā ghanavinibbhoge kate anattalakkhaṇaṃ yāthāvasarasato upaṭṭhāti.
Now lets see in its atthakatha what is nānādhātuyo vinibbhujitvā and ghanavinibbhoge
visuddhimagga-dutiyo bhago-paṭipadāñāṇadassanavisuddhiniddesavaṇṇanā-upakkilesavimuttaudayabbayañāṇakathāvaṇṇanā-739
ghanavinibbhoge kateti samūhaghane, kiccārammaṇaghane ca pabhedite.
and
tā dhātūsu ñāṇena vinibbhujitvā dissamānā hatthena parimajjiyamāno pheṇapiṇḍo viya vilayaṃ gacchanti, “yathāpaccayaṃ pavattamānā suññā ete dhammā dhammamattā”ti anattalakkhaṇaṃ pākaṭataraṃ hoti. tena vuttaṃ “nānādhātuyo … pe … upaṭṭhātī”ti
Good luck in your quest
Regards