Seems to me you are asking a few different questions in your post. As a guitarist myself Ive traveled through these and found the following usefull.
With respect to reduced gain when recording and wanting the same live vibe or sound, 2 methods ive used........
A. Buy a variac and use your live rig in the studio.
B. Search out a low wattage amp with the same or similar sound signature as your live amp for use in the studio. A fender Champ or similar seems the go for many.
I have found option B to work best for me.
With respect to the "conundrum of my own diffuse field listening requirements " .........I'm not quite sure what you are meaning here but if its hearing the guitar amp from where you are standing as a player rather that with your ear up against the grill cloth as the mic 'hears' the amp, this issue was a biggie for me when I was an infrequent studio player, and was a cause of much frustration. When someone else was the engineer, a big part of this was the different interpretation the engineer had towards the guitars sound and level in the mix. A large portion of this was my ego and wanting every nuance of my playing to be heard in the mix as I heard it in the room. Some of it was the production team not getting the overall vision of the song in the same way the band was aiming at.
It was later in my playing career that I became the engineer and by this time I had mostly grown through the ego aspect of this conundrum..........almost ;)
Firstly learning curvs like being an engineer especially for other musicians projects, grew my appreciation for the tapestry that a multi channel multi instrument recording and production is.
Re the 'diffuse field listening requirements' interpreted as room sounds perspective as opposed to close mic sound, What brought this all together for me was an evolution of intuition and the experiences of other mentors, Particularly Bill Irvine, a Melbourne engineer who i have learned a great deal from and this forum, particularly Terry's shared experience of less is more with respect to the number of mics used, and cardinal panning.
There is a hell of a lot of little, seemingly insignificant aspects, that when all are taken into consideration by the experienced engineer collectively result in a recording that is sounding real, natural, big and musical in a non fatiguing way with the effect of engaging the listener in a similar way and dynamic of that of a live performance. And stuff any one aspect up and the result is an 'F up' with respect to achieving this outcome.
I'm sure others can elaborate better that I