I hope you keep those side windows covered while measuring and listening.
For years, I've been operating under the same assumption. All the videos that I watch on YouTube say the same thing...use absorption on side wall reflection points, especially in front of windows.
This past Sunday, my wife was watching TV with me. She likes it sunny in the room, so we pulled the curtains back and opened the blinds. When she left, I put on Tool and cranked it up a little. I noticed it sounded different, like the sound stage had greatly expanded. The speakers disappeared in the room and I had about a 160 deg horizontal sound stage.
My measurements were made with the blinds closed and curtains drawn so far. I'll do some with them open.