I'm attempting to purchase a YN domestic award ticket as a 1K. I'm picking YN and happy to pay the premium over XN because there is a high chance I'll need to delay my outbound flight and SDC for a flight the next day - presumably, being in a YN fare allows me to SDC as long as there are open seats (whereas XN may run out).

When logged out I can view and select YN inventory (at 15K miles per ticket), but as soon as I select the flight and login it automatically switches my fare to the cheaper XN fare (at 13.5K miles per ticket) instead. Is there a way to forcefully select the YN fare anywhere in the UI?