My first thoughts would be to place them on opposite sides.

Ultimately, you will want to get your rock in there and see.
And play with it according to rock placement.
Secondly after you see where high, medium, and low flow areas are, you will want to adjust again to suit your coral placement. Or vice versa.

Thanks SmokinReefer, I figured I might end up with that placement. I was hoping to keep 3 sides as open as possible.

I read somewhere where someone had one on a side and one on the back for a 90 degree turbulence. I will play around with positioning when the two Nero 3s arrive with the rock and sand in the tank.

One of my two eflux Wave Pumps just died in my 28g. I was going to use them low on the bottom. That's my 2nd one to die on me so I think I'll avoid them in the future. The two Neros and the returns will probably be enough flow for softies and lps.

Might be silly but I want to share something I'm going to try. I'm been trying to figure out where to put all my Xenia and GSP in the new tank. They need to be on islands and I have a lot of it but I didn't want to waste limited space.

I've gone the Dr. Suess route and make some rock trees. I'll wrap the trunks in GSP and put the Xenia on top. Not sure if the GPS will over run the Xenia.

I'll let everyone know how it goes. Updated pics for references:

Tank: https://photos.app.goo.gl/d3xjovjMmVkwZULi6
XenGPS Tree 1: https://photos.app.goo.gl/5TBh4xnWUYY8akTR9
XenGPS Tree 3 & 4: https://photos.app.goo.gl/mxoMV8XHdeS42PdP6

Well, that's a creative solution to keeping those guys isolated!
I'd imagine they'll look pretty cool once grown in.
Hard to say who out-competes who.
The GSP can overrun the Xenia, but the Xenia can grow atop the GSP!

And I saw of pic of your setup, lots of height to accommodate those powerheads. I think they'd be fine on opposite ends.
Alternating setting to create wave action or even just random setting would work great.