Interesting. At least the Velocity is more of a 'shoulder wing' configuration, with a bit more head between the bottom of the tanks and the engine's fuel inlet, right? I suppose that with adequate sump size, fuel would always flow into the sump. I flew a BD-4 (high wing) for a while; its stock system looked very similar to that drawing, with each pair of dual pickups T-d into a fuel selector where the sump is shown in your drawing. There were numerous fuel starvation incidents when there was fuel in both wing tanks. The most popular fix was a sump in the baggage compartment for each wing tank, with a vent from the sump back into the top of its wing tank. It still had a fuel selector after the sumps, so you could keep the fuel load balanced between the wings.
On low wing planes like RV's, the main tanks are at most an inch above the lowest point of the fuselage. There's no way to gravity feed a sump, so if a tank unports (due to no fuel or just uncoordinated flying, like a slip), they *will* suck air.
Charlie