I've noticed this myself built in August and delivered in September. 2018.50 was driving more bass but from the front. I could lay in the trunk and not have a lot of bass from the woofer. I have the EQ for bass turned up and center. Setting to rear was quiet everywhere.
There are a lot of variables and things going on here. Some end up bordering on "unintentional FUD".
When you open the driver's door, the sound of the whole system will reduce. When you close the door it won't go back up unless you are already sitting in the driver's seat.
So, someone could do the following:
#1: Tune audio so it is loud from the drivers seat.
#2: Get out, go to back of car and lay down or sit next to subwoofer to listen. Find that it isn't outputting much.
#3: Go back to front door and close it hoping to make volume go back up. Return to open trunk to listen again. Still find it weak back there.
Not saying that you got hit by this "feature", but do be mindful that driver needs to be in driver's seat for volume to stay at the same level.
Note, you could open the passenger door, and adjust the volume back up before going to the back to check it...
Also, don't close all the doors or the car will shut down...
Another data point - are we comparing sub-bass or mid-bass? The front door speakers put out the bulk of the mid-bass. The subwoofer in back is more for sub-bass (like ~30-50hz ). So one really needs to have some sub-bass heavy music playing to expect the subwoofer to be outputting much. From my recollection, it seems like the rear used to be putting out more mid-bass, but not so much anymore. Another theory: did they change the EQ on the subwoofer so it has a lower crossover frequency?
When different people compare/critique the output from the rear, it is important to make sure we are playing similar frequencies through the audio system to see which speakers are playing the sounds.