My vent comes out of the bottom, per Q-200 plans, sits about 5" below the fuselage, just aft of the spar. Served me well for 2,000 hours. Naturally, everyone else's mileage may vary.
I have had mine on top for over 800 hours after experiencing problems with the vent coming out the bottom. Used a SS tube initially and then built a small airfoil shaped inlet that is about a half inch tall. Works great. The idea came from Dave Hudak's plane. I also lowered the header overflow by about 1/2" to stop the over filling problem. Be happy to send you a picture of mine and its location if you are interested.
PS just lowering the overflow may have cured the problem of a fuel loaded vent line but mine works great and would do the same again.