Calling the cybertron from above.
Has anyone even tried smaller bookshelf speakers and getting a mate to hold the speaker in their hand while one is sat in the seat in the room and play "pink noise" and get mate, to move the speaker along the sidewall at many height elevations and titled angles when placed up higher on the sidewall and back wall as well. No one tried this? That will at last give better idea on where to place the speakers and then mark the potions with pencil.
Then repeat the same ^ above while seated and get mate to stand on a chair or stepladder and hold out the small bookshelf even JBL control 1, compact/lightweight easy to stretch arms out a over a few feet while moving chair/stepladder and trying other areas on the ceiling while its facing downwards and playing "pink noise" while listening and noting on paper or laptop your thoughts for later reference use when finally fitting the speakers matched along walls and ceiling.
If you have good basic instincts
on knowing where to place the speakers?
No pun, but had to cover the beaver up.
I would just look at the speaker-size and the room and make good judgments to placing them around the room to get the most defused surround from the inexpensive cost that I paid for.