Lot's of testing today using a slightly simplified walking test method in two different speaker positions.
Sorry to be coming back in to the thread so late! (Got a lot on my plate right now...) But others have been taking good care of you in the meantime...
Anyway, I downloaded the REW files, and I'm taking a quick look at them right now. But just one quick comment here first:
But the big drawback that I immeadiately noticed was the loss of definition in the mids.
Don't worry too much about what you see in the mids and highs, since you are planning to flush-mount (soffit mount) your speakers. It's the low end that needs your attention most: the soffits themselves will do a lot to clean up things across the spectrum, but the lows are the big problem...
No idea how to explain this loss of mids but it really ruins this corner position.
With soffit mounting, the speakers are not in the corners! They are rather far out of the corners, actually. The main purpose of the "walking mic" test is to find the position with the smoothest low-end, which is the most important aspect of the acoustic response of the room, by far. Part of that is to help identify which issues are SBIR and which are modal. Modal issues do not change in frequency as you move the mic: they only change in amplitude. SBIR changes frequency, with lesser changes in amplitude. The combination of those two is a pretty good indicator of the overall room response, and the Walking Mic test helps find them both, and locate the "least offensive" spot for the mix position. The low end defines the entire frequency response of the complete spectrum, so getting the best spot for that, already goes a low way to cleaning up the rest. You might not be able to see that on the initial tests, but it's the end modal response that sets the stage for all of the rest. It "shapes" the frequency response for the full spectrum.
One final test which is interesting is another full L / R / L+R measurement from the exact mic position from the "Symmetrical Baseline" test, but with the speakers moved to the corner position.
What sticks out more obviously from this one, is the lack of low-end symmetry:
That might be due to the angled front wall, and will be somewhat attenuated by well designed soffits.
I thought this might illuminate which issues are SBIR and which issue are modal.
Not so much:

It's the walking mic test that is most useful for that.
There's a lot of data here and I'd love it if anyone had the time to take a look at it
I'll take a look at that, and try to respond shortly, but... :
At the moment my initial position still sounds the best to me, I'm guessing because of the flatter mid response.
Don't rely too much on your ears at this stage! REW can reveal a whole bunch of issues that you can't hear consciously, but that do have a large effect on your overall perception of sound (eg, directionality, sound stage, stereo image, focus, etc.) In other words, you can't actually detect what the problems are with your ears by just listening, even though you can "sense" that something isn't right, because the effects you are listening for are actually CAUSED by your own ears! Psycho-acoustics is the science of how we humans
perceive sound, as opposed to how the sound actually is. The interactions between sound wave patterns, your ears, your head, and the room, cause your brain to interpret sounds in a certain way, which isn't necessarily the way the sound really is. That's where REW comes in: it shows you how the sound really is, then you can understand how your brain misinterprets that sound. That's why you can't hear it: because by the time it gets to your conscious brain, your ears themselves and he "unconscious" pre-processing that your brain does first, has already modified what it is going to tell you. Thus, it is impossible to identify what the problem is just by listening, except to say that it "sounds off": So, for example, you might notice that the sound stage is too wide, or not wide enough, but be unable to figure out WHY just by listening, but REW will show you the early reflection that is causing you to "sense" that, and it will give you enough info to determine exactly where that reflection is coming from. Your ears cannot do that, because they don't have the ability to even hear early reflections directly! But a mic does.....

You'll use your ears a lot more once the initial problems are taken care of, after the soffits and initial treatment are in place, but you can't trust them too much this early in the game.
- Stuart -