There are only two awards levels for one-way TATL D1 awards - 80K and 320K. So when there is no married segment availability for 80K, you'll jump to the 320K level. The 80K awards also have a 90-day advance purchase requirement. There are other D1 award levels available, but they require a roundtrip purchase. I'm surprised they would combine another award with the D1 awards as they prohibit end-on-end combinations in their fare rules. Although they will quote combined awards on one ticket if you have a layover of greater than 24 hours to create a fare break. You can see this with a multi-city search if you specify the second segment two days after departure (since you arrive the next day on TATL flights) which creates the >24 hour stopover needed to combine fares.