Taxes/surcharges queries

Just a couple of questions which no doubt someone here will know the answers to
:
(1) If booking an outright Upper Class reward LHR-LAX return (dates in Sep 2013) the grand total for tax/fees is £545.25. However if using cash the grand total is £568.85. I can see this is due to 'US' (USA Transportation Tax) and 'XF' (USA Passenger Facility Charge) not being included if it's a reward. Any ideas why?
(2) If booking just a one way reward the grand total for fees/taxes is £728.30 which clearly is far more than half the total compard to the return. Why?
Cheers
James

(1) If booking an outright Upper Class reward LHR-LAX return (dates in Sep 2013) the grand total for tax/fees is £545.25. However if using cash the grand total is £568.85. I can see this is due to 'US' (USA Transportation Tax) and 'XF' (USA Passenger Facility Charge) not being included if it's a reward. Any ideas why?
(2) If booking just a one way reward the grand total for fees/taxes is £728.30 which clearly is far more than half the total compard to the return. Why?
Cheers
James