Why didn’t you (or won’t you) test for radon in the crawl space? - WNC Independent Labs
The concern is long term exposure, so the test should be conducted in an area where people will spend a significant amount of time – most people do not spend a significant amount of time in the crawlspace.
Additionally, houses (especially newer homes) are more airtight than most crawl spaces, making it easier for radon to build up in the home.
17 January 2022 Radon Testing FAQ