Originally posted by alamo5000 ... My questions and/or topic of discussion is NOT about equivalence although I will reference angle of view to some degree.
...
My theory is ...
Your question is
all about the equivalence theorem.
Please get over some of the opiniated discussions and actually learn what it is all about. All of your questions will be answered, and more. There is no need to have yet another theory about the topic.
I'll give you a pointer to an article I wrote about it but won't have time to participate beyond this point.
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LumoLabs -- Camera Equivalence -- Whitepaper
Nevertheless, here is the answer to your question:
Yes, the FA31 (on FF) will bring out your subject "more prominently" than the DA21 (on APSC). But it isn't a property of the larger sensor or larger focal length per se.
E.g., the DA21 at F3.2 on APSC, and the FA31 at F4.8 (at twice ISO) on FF will produce indistinguishable images. However, at apertures between F1.8 and F4, the FA31 will render your images with more 3D "pop" (shallower depth of field) than the DA21 could provide. In the example you mentioned though, you did not reach the apertures where this matters, so you wouldn't have seen a benefit coming from FF there.
One more note, I know, you didn't ask, but ... When set to produce indistinguishable images, e.g., DA21 at F4 and FA31 at F5.6, then the FA31 (which is a stunning lens to start with) has much less aberrations. Even and contrary to common belief, in the corners. But the DA21 is a much smaller lens, so if only needed at above F4, I wonder if I wouldn't prefer the DA21 and an APSC body.