I recall reading that Tigerair ferried an A320 from Clark (RPLC) to Melbourne (YMML), which is a great circle distance of 3444 nautical miles (I have no idea of what the winds were). My guess is that Avalon was their alternate.
I thought A320 only held 18.9 tonnes of fuel; at least that is what the copy of the manual I have seen suggests.
5250 miles (even statute miles, or 4562 nautical miles) seems very optimistic with anything less than about 250 knots tailwind.