OK, the bass build-up is definitely right under the peak of the ceiling where it joins the wall. When time next permits I'll put a bass-heavy track on again and go up in the loft to see if there's a build-up of bass there as well, or up in the peak.
If so, then I guess that's where the next bass traps go. I can't add any more downstairs because there's no free space in the high-bass areas, but it would be really convenient if I could put them upstairs where the piano was supposed to go (but closer to the wall).
I'm seriously thinking about revisiting the room layout -- maybe start by putting an M60 in the current listening position then doing a sub crawl to see where the bass ends up and hopefully find a potential speaker position.
I'm already envisioning some kind of bizarre outcome where the ideal speaker position is 11 feet off the ground in the living room and the ideal listening position is 4 feet up a tree out in the yard
