best placement of powerhead in a 20g long?

So these past few weeks ive been experimenting with different placements of my 2 hydor koralia 425s and also the direction that my duckbill return (~300gph) faces, to get suspended detritus to lead toward my hob aqueon overflow box. So far all i can seem to acheive is getting little cyclones of detritus on my tank corners(bottom glass) and all suspended particles get close to hob overflow but either get pushed away or drift rigt past.

Has anyone had success with a specific placement of a two powerhead setup with return in back left corner in a long shallow tank 30x12x12". I can move overflow box anywhere i want on tank. Return kinda has to stay in left back corner.

Thanks for any ideas
Scott