Thanks, I knew about the direction change, although the last couple of trips on this route have originated in LA so not a factor. On a much earlier trip we boarded at Burbank, but they only opened one door on the 7 car train further down than ours. Long walk with kids and luggage to the open door, then all the way back while the train was moving (single level consist too). Every other trip has been from an origination point (San Diego, LA, San Luis Obispo), so all doors open and easy to find BC car.
The recent rule-of-thumb seems to be BC car adjacent to engine, train pushed southbound to LA, then pulled southbound to San Diego and then the reverse, so sounds like what you've described exactly. We're a lot older now and my wife takes too much luggage.