Try this article, and skip to the last few Powerpoint slides:
“Subwoofers: Optimum Number and Locations”, Todd Welti, Harman International.
https://www.harman.com/documents/multsubs_0.pdf Being pithy, Todd says that 4 subwoofers are enough.They're in different locations from what you posted in 2021, and maybe it's worth a couple of weekends trying them out.
He modeled 5 and even 5000 subwoofers in the same rectangular room, but 4 effectively gets you there. There have been several loudspeaker designers (including Axiom's Ian) who've rehashed 4 as the magic number for multiple seating positions, but they might all be citing Todd's work.
I don't mind experimenting. I moved the sofa and lounge chair back to the natural layout of the room, which meant everyone sat off-center from the TV. So I switched the location of the sub and the TV+3 front channels for a couple of months. It was an audio step backwards with some undesirable wall reflections and the loss of 6 dB of subwoofer corner gain (effectively requiring 4x the amplifier power to maintain the same listening volume), so I reverted it last week.
