For me, having the intake of a canister slightly above the intake of a HOB filter helped stretchout the time inbetween cleaning my canisters out since the HOB caught most of the floating stuff.
I personally prefer the following set-up for canisters, since it circulates the water well and flushes debris to the outlet:
Spraybar on a side panel (let's say on the right). It sprays water diagonally from the right top to the bottom left. The filter outlet is positioned on the same side as the spray bar (here: right). This causes a horizontal water flow from the bottom left to the bottom right, into the outlet, and out of the tank. This horizontal flow takes all detritus with it on its way.
Check out my set-up below. Even wolf fish poop gets flushed to the right back corner.
An AC won't affect that flow too much, if anything, I would put it on the left back.