It’s a personal preference regarding how many speakers/subs we want to fit in our rooms. No right or wrong, just curious.
Of course, the size of the speakers and subs and placements (on floor vs on wall vs ceiling) also make a significant difference.
If each speaker is a 60”-70” tower or each sub measures 24” wide, fitting them into the room will be more interesting.
And having speakers and subs in-wall, on-wall, in-ceiling and in-cabinet definitely makes it easier to fit more speakers in the room.
For a 20’ room, I can see going with 5.x.4 or 7.x.4.
Depending on the size of the speakers, I just think it’s overkill doing 9.x.6 in a 20’ room if using bigger speakers.