all I know is that my studio is like a narrow hall with the stage at the end . Side walls are angled and beveled out in an irregular fashion. It used to be smaller, around 20 ft lol. I had it treated at first and it still did not have the sound I was looking for. I still heard harsh sounds reflecting back from the door end. My door is metallic and walls are thin have some more reflective and vibrating surfaces.
I had my room analyzed by an acoustic engineer and that’s when he mentioned the same wavelength thing to me. He suggested extension if possible. I confirmed it with @AlphaVictor and had my studio extended 16 more feet (my dad is a contractor so I didn’t really have to pay much)
once I extended my studio, (same acoustic treatment) I was blown away by the sound. Everything just seemed to flow, there were no harsh or tinny sounds anymore. It was a very sweet sound like a mini concert hall. So there must be some truth to the theory. A practical test .
Now true test would be if I bring my wall back in by a few feet, closer to a partial wavelength, if the sound worsens, it would prove something.