Fuel Management issues

[glazmax]

In my attempt to provide some fuel control settings I discovered the properties:

controls/engines/engine/feed_tank

which should possibly define the tank, the engine takes fuel from?

controls/fuel/tank/to_engine
controls/fuel/tank/to_tank

which define either where to pump the fuel?

Now my question: Are this properties functional since I played around with different values for them (int -1,0,1..) but experienced no change?

Stay fueled,
markus