I'll throw this into the debate: The Eheim has a spray bar ( on can only set it vertically) and the Fluval 405 has a regular output nozzle. The 405 creates a lot more current.
Right now i have the output of the Eheim and input of the 405 in one corner, and the opposite in the other.
Seems a little unbalanced to me???
Perhaps put the Fluval output in the far right corner and the Eheim spray bar on the left, but a little close to center with both inputs centered...
I have a planted tank btw, not sure how or if that changes anything.