The Empire Builder is a little different - because of the Seattle section + Portland section, the Portland sleeper will be on the opposite end of the train as the Seattle sleepers. However the Portland sleeper is always known as part of train 27/28 even east of Spokane.
My experience has been that the Seattle section will have sleepers at the head end (behind a baggage car), then dining car, then Seattle coaches (two or three depending on season), then the Portland Sightseer, then the Portland coaches (usually two), then the Portland sleeper. One of the Portland coaches will be a coach/baggage.
Else, coach passengers would have to walk through the sleeper car when the train is combined to access either the Sightseer or the Dining car; or the train would require significantly more switching in Spokane to break apart the train consists. Keep in mind that the station stop in Spokane is at midnight, so it's not a good idea to be switching cars around when people are trying to sleep. (On a positive note, you don't have to worry about as many passengers trying to get on/off the cars.)
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Erik Halstead - Portland, Oregon