Great question! Been wondering the same. Currently I have mine set to get the water spinning (they all point off to the left), thinking that by circulating the surface clockwise I'll drive surface gunk past the skimmer, where it's more likely to all get sucked in (and that is pretty much working in my pool). My deep end eyeball is pointing a bit down, to stir up the bottom, too. But my pool is rounder, with three returns spaced evenly around the pool, so not sure how well that would work with your more rectangular shape with returns only on one side.
I would have to guess mixing would benefit, too, by rotating the water around the pool.
I have a prevailing wind in my area, which, unfortunately does not push stuff towards the skimmer. So on a windy day all bets are off. Does your skimmer get any help from the wind?
I'll be following along with what others suggest...
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PS. Was your pool built without main drains? I just had mine removed, as they were never configured to move water, and were just hanging up my cleaner. I'm hoping I don't regret that decision. So far, I think my circulation is fine.