I watched clip on Youtube not long ago, the guy seemed very knowledgeable in what he was doing but one thing he did say was if you put the inlet very close to the outlet, basically you are only filtering a small amount of water.
He was saying the water coming in would be sucked out again very quickly so it needs to circulate, so have the pipes far apart and if possible have the outlet sending the water in a circular motion so it goes round the tank before it gets to the inlet again.
Exactly why I would put a wave maker directly under/next to the inlet stream. I also have one to put at the other end of the tank to circulate water back to the out flow.
Thanks,
Steve