No more guesses. I'm on AMTK 790 as I type. I boarded in SLO in car 1, business class (BC), but prefer the Superliner cars over the Surfliner cars a bit, so I moved to car 2. The trailing half of the car was facing what would be backwards, to I moved to the front half a couple of rows in front to the curtain. Still with a few minutes to origination departure I created a nice mess with a PC, phone, associated cables, lunch, etc., etc. The service attendant then appeared from car 3 and asked if I was to be in BC. Answered in the affirmative and she advised I was in the wrong section by a wee bit. Then she closed the curtain. Although I chose to stay put, she asked of my refreshment of choice and brought me the goodies.
As the "experiment" with a second BC car was to end something like December 4'th, it's clear they've decided to carry on. My experience over the last few months since inception is the Superliner was staying relatively empty while car 1 would get packed (communication to passengers could have been and still be improved). Clearly an entire second car is not needed for BC much, if not most, of the time and they are modifying the BC size per train based on reservations.
--Bill