Any particular combination you're having problems with? I can generate mileages from St Louis to JFK (892 miles (1427 km)), Hanoi to Singapore (1366 miles (2185 km)), Brisbane to Moranbah (485 miles (776 km)) and the Seychelles to Abu Dhabi (2009 miles (3214 km)) without dramas.
MEL-LHR, MEL-SFO, SYD-JFK etc etc. I said flights requiring a connection.