Hey guys, so after some calculations and scheming - here's a preliminary plan for the setup and absolutely necessary treatment.
Legend:
Orange - Corner BASS traps (foam) or perhaps later DIY membrane-panels.
Green - RFZ diffusors for hi-midHi reflections.
Purpleish - IkeaBookshelf with randomly stacked books/records and custom perforated 37x33x33 cubes, perhaps I'll figure out a way for a new type of DIY mini membrane-panel-cubes
Quick recap - RFZ sweetspot and bass management at sweet spot are main goals. Even bass response in entire room not necessary.
The JBL's are spaced approx. 70cm from side walls, and about 2m from front wall. At the current position they will also avoid the lowest part of the slant and thus hopefully also immediate reflections from above. The slant goes to about 3,2m+ above my listening position - which should give me at least some wall-to-floor reflection break.
Also I plan to foam-treat the ceiling slant immediately above the JBL's.
I'll be sitting about 30-35% from the back wall with the Bookshelf right behind me.
What do you think?
Room dimensions: 496x346x(1-3.2+)