When thinking about sub placement, i always think of a church i used to play at that was in an awkward rectangular room, but the stage and soundbooths were on the long sides, not the short.
Anyhoo, the church threw all the money at the PA.
Mains and subs were flown. Three subs, one center and one on each side.
But they never sounded right. There was cancellation everywhere.
They fixed the problem by getting rid of the subs on the sides.
The center sub was enough to carry the room, and the dispersement was perfect to get low end to every seat.
So now i look at it a bit like “less can be more” when it comes to subs.
And too often, i see the opposite approach, especially at some of these smaller gigs, similar to OPs.
Granted, being outside, that does also affect the low end.
Anyhoo, just thought i’d share, sometimes fewer subs is the right answer for the best low end.