Locate specular hit points, see the early-reflection comb filter, and toggle a virtual panel to flatten it.
Primary reflection (floor) arrives 3.9 ms late — that comb filter is what you hear in the highs.
Preview only — open the 3D builder for full placement, treatment, and analysis.
Sit at the listening position while a helper slides a mirror along the side wall. Where you see the speaker in the mirror is the first-reflection point — treat that spot to cut early energy under ~15 ms that causes comb filtering.