I was looking at that teardown myself to see whether this was the case, and I don't think it's enough information to say -- that's a teardown of the model with 16GB of RAM, so it's not impossible that the 8GB model might leave some of those areas empty rather than switching to lower density chips.
It's also possible that it varies depending on DRAM prices. You might have models with 8GB populated single sided and others double side. Same goes for the 16GB models.