When you're measuring some quantity that originates with several different sources, do not assume that when the amount from one source exceeds another's, that the other's becomes irrelevant.
We see this constantly in camera land. Blah blah noise is greater than blip blip noise so we can ignore the latter. The lens is soft so there's no point using good filters. Etc.
This stuff mostly either adds together, or combines in counter intuitive ways. But it almost never vanishes.