HOWTO: Airspy mini and Airspy R2: Piaware / dump1090-fa configuration

Currently running Airspy on a Raspberry 4 for testing purposes.
What i have seen is a difference in max. number of aircraft count:

On the Aircraft chart it shows 204 as max:

But the Airspy graphs reports 215 as highest aircraft count:

Also the average count differs.
Where does that difference come from? Different things?