The mass-concrete pillar behind the left speaker and the closet beside the right speaker present different geometries and reflectivity. If you can manage it, I suggest rotating the room configuration 180º so your main speakers are against the flat wall (which is the back wall currently).
After that, in my experience those deep FR dips around/below 100 Hz are likely confluence of lateral, tangential and/or oblique room modes at the problem frequencies. Try moving the speakers laterally (from a narrow starting position, then stepping toward the side walls say 200 mm (8") increments or similar, measuring FR at LP after each step to see how those nulls behave. I've been able to significantly mitigate similar issues that way. Your room is small, and you still have the asymmetric entry nook, but hopefully you'll have more scope/consistency doing this against the flat wall than the current front wall which has more asymmetries and obstructions.
Edit: looks like @Chromatischism was on to this already
After that, in my experience those deep FR dips around/below 100 Hz are likely confluence of lateral, tangential and/or oblique room modes at the problem frequencies. Try moving the speakers laterally (from a narrow starting position, then stepping toward the side walls say 200 mm (8") increments or similar, measuring FR at LP after each step to see how those nulls behave. I've been able to significantly mitigate similar issues that way. Your room is small, and you still have the asymmetric entry nook, but hopefully you'll have more scope/consistency doing this against the flat wall than the current front wall which has more asymmetries and obstructions.
Edit: looks like @Chromatischism was on to this already
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