Message rate vs Aircraft

This “thing” is puzzeling me for a while now.
I have two receivers, both piaware v3.1.0
One of them (RPi-01) has a higher antenne, so it receives a bit more then RPi-02.
But: When I look at the message-rate, it is lower.
At this moment:
RPi-01 : Aircraft 154, Messages 1114/sec
RPi-02 : Aircraft 116, Messages 1115/sec

I would expect that the more Messages, the more aircraft ?

Higher message rate does not always mean higher plane count. Look at the gain adjustment topics. Some settings get higher message rate, some get higher range, and some get higher plane count.