Hmm. . .The lack of reflections could be it. But I'll be honest with you. . . I have done the same thing before, and I only moved my speakers 1/16".

I think that even with this system of exact measurements, it's still all to easy to be off 1/4" or more. I have now two points that I measure from, and I can NEVER get both of them to line up right, even though they are equidistant from the side walls. So my walls are off. . No problem.
When I measure from the one point, and it shows right within 1/16", sometimes it really isn't right, and I can tell by just listening. The magic is GONE. Then when I measure from the other point, and find out I am 1/4" off or more, I start to wonder if I am THAT inadequate, or insane.

But when I line it up from the second point, it comes back.
And what you describe is what happened to me a week ago. I decide to move my Piegas to get a bit more bass. Holy cow that really screwed up EVERYTHING! The emotion vanished from the music. Sure, the bass was there. . . And sure, they were within 1/16". . Or so I thought. . .
Then I moved them back out where they were, and measured. . Still no emotion. Sucks. . . So I made a new midpoint closer to my chair. Voila. Even though the midpoints appear to be equidistant, they are not. This is very frustrating, so once you get it right, leave them alone! hehe
Actually, I am going to move mine again b/c I want a slight bit more width. That will begin the nightmare again.
It makes me wonder what kind of hell people live in where they have never done this measuring method, and never known what their system really can do. It's probably more difficult when you DO figure it out b/c once you hear that, you can't go back. They are likely better off not knowing. . hehe
Gosh I am in a rambling mood today!
Sorry. .
B