Somebody at airbus said off the record that....
Those kind of things need to be taken with a grain of salt.
Physically, the collector cells lie between ribs 1 and 2, the upper and lower skins, with a one way valve for (inner) wing tank fuel to flow into the collector cell but not out. The cells have 2 pumps, fore and aft placed in opposite corners.
Once the fuel resides in a collector cell, the only way it exits that cell is through a pump to an engine. (It won't slosh/drain over to the other wing in a steep turn)
FIT would need to read 0 before the engine would flame out.
Having said all that, I understand that you can in fact flame out the engine but you would need to hold an fairly excessive angle in pitch and roll attitude or high g load for more than a few minutes, or be inverted.