RE: Evolution engine
In each case where I've had an inverted engine problem, the "problem" turned out to be tuning or a not fully broken in engine.
I've never had to invert or adjust the tank with my tail draggers to compensate.
Once I had the plane properly tuned siphoning would occur very slowly to the point that it is a non-issue with the throttle at idle.
Remember to tune the engine with approximately 1/3 of a tank of fuel, and not with a full tank.