https://thepointsguy.com/guides/how-...-domestically/
So for example there's one daily flight between LAX-ATL each way on a 777 (which are all internationally configured with D1 and PS seats, but serve domestic FC service, therefore not the true D1 international level service like LAX/SFO-JFK) which I've recently done a 4 times, twice booked in D1 and twice upgrade the the C+ service in PS seats, which is much nicer (especially compared the 767 I had going to BRU where it's the old D1 seats and regular C+ seats)