The tank should be set up so that the vent line goes from top-forward inside the tank and then exits through the bottom of the fuselage/cowl. That way, fuel cannot siphon out. Yes, in some maneuvers you'll lose the fuel that in that small length of fuel line, but it won't be enough to matter. Since many maneuvers will have positive "G's", fuel won't come out at all.
The correct fuel tank placement should be such that the centerline of the fuel tank is level with the center of the carburetor or slightly lower. It is common for the tank to be too high.