It's not possible to know if it's at a reflection point without more information. Maybe he sits at the rear wall?
How do you know it changes the sound directly beneath the beam? And if there is a sound change there, how do you know it's not coincidence?
I had a beam that came deeper into the room. I'm not sure whether the beam ever did much to the sound, but I never had enough time to test. At one time, I had hung a Realtrap from the ceiling at what I thought was the main ceiling reflection point. Unfortunately, not only did I change speakers (VMPS RM40 to Salk HT3), I also completely redid the room and took the Realtrap down. And then I had 7 channels of music and surround sound, but even with 2 channel and sitting right in front of the beam, I couldn't tell that there was any effect caused by the beam. But, I also never tried to find an effect, either.