Radon tests are overrated. But if you want builder to upgrade to an "active radon mitigation" just keep running by these sensors :), there will lot's of be "radon spikes". (Most market houses will never pass radon test as long as kids live there.)

Honestly - you should lock the house out [day] for as long as monitoring equipment is operational if seeking to know true values.

It's either overrated or the 2nd leading cause of lung cancer depending who you listen to. Europe has action levels 1/2 of what the states do, for what it's worth.

Great job installing the passive system. Personally, I would go ahead and move in and monitor radon with a longer term alpha track type tester. The more widely available short term tests will be all over the place in results.

All about radon is a good GBA article.