By far the largest impact I’ve observed on my CO2 levels are from the hvac. When the fan is on the levels go down and tend to stay down, so I usually leave it on circulate which runs every ~15 mins (based on the graph structure). I use an SCD30 in the corner opposite to where I sit.

Also important is using a direct CO2 sensor (NDIR or photo acoustic) and not eco2 which can give false positives from other things in the air.