I have often overlooked this myself. A controlled test can't account for this since it is based at a "point in time" which can be influenced by several biases including how an individual was feeling that day.
I agree, my system often sounds much better when it's 70 degrees outside, I have my windows open, and there's a nice breeze.
But the controlled ABX test isn't about which sounds better, it's about can you tell the difference between A and B. As long as the conditions remain the same throughout the trial, it doesn't matter if you're having a good day or not.
