Right now the air quality sensor is in the basement, and the purifiers I'm comparing it to are upstairs. It's not a fair comparison, it just "seems" to be reporting using a different scale.

My plan is to put the sensor near one of my STARKVINDs and see how the numbers compare. This will tell me if they're measuring the same thing and reporting it at the same scale. Once I understand what the sensor is telling me a bit better, I'll put it in a more useful place. Your suggestion of putting it closer to where you sit is a very good one.