Am I imagining this? It seems that certain somewhat older film stocks have a grain characteristic whereby if well exposed, the negative seems relatively fine grained, but where less exposed (such as in shadows) the grain is much more pronounced. I shot some Fuji NPS 160 (35mm) and it seems to have this issue, where Portra 160 does not. It's kind of frustrating, because different parts of a single image may have different graininess.

The mystery to me is --- what is the innovation that seems to cause this to be less of a problem with more recent films?