I know, having the returns inside the box means a larger box. The advantage is more surface skimming and less water column draining.
I'm not having any luck right now finding a pic to demonstrate the flexibility of having the lines on the box sides.
What I'm getting at though is you have the back nozzles pointing to the corners across the surface and the others can be pointed more forwards, and down-ish if you like. It gives you more flexibility to find those flow sweet spots.
Back flow is definately something to consider.
I opted for over-the-top return lines to solve this issue
Because my overflow is offset, I have one nozzle left and a Y for 2 nozzles on the right.
