Searching for reward flight

When i search for return reward flights and the result comes back that there is no availability and i am asked to try alternative dates, a different cabin, etc., why can't the website just display the available dates like it used to? One trick i have learned is to search for reward seat availability as a single journey then the availability calendar does appear for the entire month. The only problem buying two single tickets , say LHR to NYC and NYC to LHR in UCpper Class is that the taxes are GBP 603 versus GBP 432 On an Upper Class return ticket.

From the 'Which kind of ticket would you like?' select 'Show me all cabins' and you should get a satisfactory view.

It generally helps to specify the start airport as LHR or LGW as appropriate rather than the more generic 'LON'. Same with New York - select JFK or EWR rather than NYC