If your room has a thick carpet, heavy curtains and other textiles. This can explain the "suck out" in the higher FQs. Otherwise you should have a closer look at your rig.
From the diagram you can also see that you have a peak at 70, then again at 140 and 280. Same thing with the dips a 100, 200 and 400. Those are a mathematical result of the measurements of your room. You will not be able to make them go away - but you can make them less pronounced by speaker placement. The long decay is a thing for acoustic treatments.
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