Thanks for the sharing.
Okay, so now we have a common understanding that Rupa is form, a materiality quality.
Khandha means aggregate. So, grammatically Rupakkhandha is Form aggregate, an aggregate of material quality.
I don’t see how it related to mental quality.
In Visuddhimagga, it was stated that:
"Herein, all kinds of states whatsoever that have the characteristic of “being molested” (ruppana) by cold, etc., taken all together should be understood as the materiality (rúpa) aggregate.
- That is of one kind with the characteristic of “being molested.”
- It is also of two kinds when classed as (a) primary entity (bhúta) and (b) derived [by clinging] (upádáya).
Herein (a) primary materiality is of four kinds as the earth element, water element, fire element, and air element. Their characteristic, function, and manifestation have been given under the definition of the four elements (XI.87, 93); but as to the proximate cause, each has the other three as its proximate cause. 
(b) Derived materiality is of twenty-four kinds as eye, ear, nose, tongue, body , visible datum, sound, odour, flavour; femininity faculty , masculinity faculty , life faculty , heart-basis; bodily intimation, verbal intimation; space element; lightness of matter, malleability of matter, wieldiness of matter, growth of matter, continuity of matter, ageing of matter, impermanence of matter, and physical nutriment."
If I understand your posts above, you rendered what was seen, heard, smelt etc. as mental aspects. But according to scripture, these things are under Rupa too.
I learned that in Abhidhamma, the four ultimate realities are Citta, Cetasika, Rupa, and Nibbāna. So, mental aspect must be referring to Citta (viññāṇa) and Cetasika (vedana, sañña and sankhara).