Are you sure you have a Centurion and not a Platinum? Centurion gives you the upgrade at booking. I've run into situations where the PTS/FHR rate is higher than what I can get elsewhere, but those lower rates don't include the upgrade eligibility or FHR amenities. If the cost is much higher for FHR, I just use the normal American Express Travel, which guarantees you the lowest rate (no FHR though).