I don't know how 'seasonal' it is, but every time I've taken the Texas Eagle/Sunset in car 421 it's always had a St Louis coach at the back end CHI-STL. Until a couple years ago, the through sleeper used to be at the back end all the way STL-LAX. I don't know why they changed the order, but now the through sleeper is directly ahead of the diner as far as SAS, and on the rear to LAX. It's the same way going back.
As far as sleeping through the switching at SAS, sometimes I sleep through, other times I'm outside watching. It sort of depends on when we get to SAS, if I'm still up and around, etc. Interestingly, there seems to be some variability in switching at SAS. I've been aboard when the through sleeper and coach were at the rear of the Texas Eagle were pulled off not too long after arriving SAS, wyed, and then held 'out of station' until #2 arrived and it was added then. This past May, I'm not sure of the switching maneuver involved, but how they managed to get the through coach and sleeper back together at SAS I don't know. But...somehow, in the process, the sleeper was not wyed, so I woke up travelling head-first in my roomette rather than feet-first when I went to bed. I usually make up my room myself, as I have medical issues that require I make into a chaise-lounge and use my suitcase with a couple of blow-up pillows as filler between the seats. So, when I got up, I threw the bedding up top and when I went to take a nap, made it up facing forward. I'm sure the car attendant would be more than willing to make your bed facing 'forward' whenever you please. Even more interesting was going the other way this past May. After they switched the cars from #2 to #22 and ultimately boarded passengers, they wyed the entire train BEFORE leaving town! Maybe they came in late, maybe a switch crew was unavailable, who knows? But by the time we left SAS station the 2nd time that morning, we were already down 20+ minutes as I recall.