The inboard side on a full fuse plane is traditional for several reasons:

1. Centrifugal force helps keep the fuel in, if needed. If you make sure the lines are above the tank level, then it should not siphon on the ground, but then when you fly inverted....
2. You want the vents in a high pressure zone. If you fly with any yaw at all, then on the outboard side, the air pressure will be lower.
3. If your engine is mounted inverted, then nearly all side exhaust engines will have the exhaust on the inboard side. This makes hooking up a pressure line, should you decide to try that, much more feasible.

There may be other reasons as well.

Dave

If you had two vents venting outboard , youd get one syphoning
, at times .