Help deciding on appropriate measures

[molybdamu]

Hello, new here to the forum. I recently started on the journey of room acoustics thanks to this forum and finally feel like I have a couple questions that are precise enough for a thread.

My room is not a single purpose listening environment and is filled with a bunch of bookshelves and closets on the sides and a 19" rack, desk, MLP and a big soft couch (second listening position) on the center axis. Adam T8Vs are positioned on stands fairly close to the almost symmetrical windows.

Now I was surprised and glad to find the decay in this room to be very even and short (200ms) without doing anything:

A smattering of 32 band PEQ and things look and sound quite lovely I think apart from that dip at 4.5k-8k which I can't seem to get rid of:

Now the pain points are of course in the bass region. Blue is without, green is with EQ, smoothed to 1/6.

I have the space for 50cm of absorption on either side in the front third of the room and am considering building slatted Helmholtz resonators which I'm modelling using acousticmodelling.com, such as this here. So, questions:

• is it realistic to attack the excess decay at 35Hz and 55Hz and the modes centered at 72 and 125 using HR tuned to be as narrow as possible?
• supposing that's effective, would that lead to the bass response being more even across the whole room, not just at the listening position?

Additionally, here's the two monitors by themselves with EQ, left in green and right in red smoothed to 1/12:

• how come the left is so much more broken than the right?
• should I try moving the monitors around until they activate the same modes? This may be impossible because the building is old and very uneven. Most surfaces are noticeably tilted…
• the monitors each have their own PEQ based on their solo measurements; is this completely backward? The weirdness from 4.5k on in the L+R measurement is not present here.

Thank you for your time!