The water fill just fall down as soon as it escapes the top so there will be no useful effect. It makes almost more sense to bypass the center inlet.
Another problem will be that you have to use a high fill level because otherwise you will get problem with the air that will be sucked back into the loop again.
Okay, thank you, but I see no other possibility than mounting it horizontally at the top in my FD Define R6. I will probably get an XSPC Photon D5.