rudderrat
Pages 16 and 17 of that .pdf link show technical differences between A320 and LR types - I don't know enough to say if that is the reason for the difference in X-FEED management.
Regarding
TyroPicard - I don't intend to run out of fuel - but to land with more than 30 mins useable fuel with both engines running,
you are discussing L+R TK LO LVL, this warning occurs with 30 minutes of fuel remaining.