I'm pretty sure that the LFG is based on total price (minus any booking fees that may be charged by services such as Expedia, Travelocity, etc). Thus, the comparison should be made between the final price on CO.com and the final price (minus the $10 or so booking fee) on the other travel website. As was stated earlier, you must actually purchase the CO.com fare (not using miles) to qualify for the LFG.